# What's the next number in this sequence? (Strictly mathematical) **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [August 15, 2001, 4:50pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411 "2001-08-15T16:50:46Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![RTFirefly](https://avatars.discourse-cdn.com/v4/letter/r/c77e96/32.png) [@RTFirefly](https://boards.straightdope.com/u/RTFirefly)\ **Post date:** [August 15, 2001, 4:50pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/1 "2001-08-15T16:50:46Z")
Since there hasn’t been a sequence yet on the other thread dealing with numbers _as numbers_ (as opposed to stand-ins for subway stops, speech patterns, and whatnot), I thought I’d start a thread which restricted the number sequences to their numerical properties. Whoever guesses the next number in one sequence correctly (with explanation) gets to provide the next one. Let’s lead off with something reasonably lite: 1,5,13,29… ---
**Author:** ![pldennison](https://avatars.discourse-cdn.com/v4/letter/p/9fc29f/32.png) [@pldennison](https://boards.straightdope.com/u/pldennison)\ **Post date:** [August 15, 2001, 4:54pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/2 "2001-08-15T16:54:31Z")
> [@](#): > > \*Originally posted by RTFirefly \* > \*\*Since there hasn’t been a sequence yet on the other thread dealing with numbers _as numbers_ (as opposed to stand-ins for subway stops, speech patterns, and whatnot), I thought I’d start a thread which restricted the number sequences to their numerical properties. > > Whoever guesses the next number in one sequence correctly (with explanation) gets to provide the next one. > > Let’s lead off with something reasonably lite: > > 1,5,13,29… \*\* 1. Each number is the sum of the preceding number and a successive product of 4: 1+4=5, 5+8=13, 13+16=29, 29+32=61. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [August 15, 2001, 5:06pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/3 "2001-08-15T17:06:47Z")
> [@](#): > > \*Originally posted by pldennison \* > \*\*61. Each number is the sum of the preceding number and a successive product of 4: 1+4=5, 5+8=13, 13+16=29, 29+32=61. \*\* I think you mean powers of two. ---
**Author:** ![armedmonkey](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@armedmonkey](https://boards.straightdope.com/u/armedmonkey)\ **Post date:** [August 15, 2001, 5:30pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/4 "2001-08-15T17:30:44Z")
> [@](#): > > \*Originally posted by RTFirefly \* > \*\*1,5,13,29… \*\* alternate answer = 47 This will work if, and only if, you consider 1 to be a prime number (which it really isn’t). The sequence goes like this: name a prime number, skip **1** prime #, name another prime #, skip **2** prime #'s, name the next prime #, skip **3** prime #'s, etc. Damn, wait, if you consider 1 a prime number, then 2 would have to be considered prime as well, which throws the whole thing off. Oh, well. It holds if you start at five and skip two primes. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [August 15, 2001, 5:43pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/5 "2001-08-15T17:43:39Z")
> [@](#): > > \*Originally posted by Beeblebrox \* > \*\*Damn, wait, if you consider 1 a prime number, then 2 would have to be considered prime as well, which throws the whole thing off. Oh, well. It holds if you start at five and skip two primes. \*\* 2 is prime. ---
**Author:** ![Manduck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/manduck/32/256_2.png) [@Manduck](https://boards.straightdope.com/u/Manduck)\ **Post date:** [August 15, 2001, 5:56pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/6 "2001-08-15T17:56:19Z")
> [@](#): > > \*Originally posted by pldennison \* > \*\* > > > [@](#): > > > > \*Originally posted by RTFirefly \* > > \*\*Since there hasn’t been a sequence yet on the other thread dealing with numbers _as numbers_ (as opposed to stand-ins for subway stops, speech patterns, and whatnot), I thought I’d start a thread which restricted the number sequences to their numerical properties. > > > > Whoever guesses the next number in one sequence correctly (with explanation) gets to provide the next one. > > > > Let’s lead off with something reasonably lite: > > > > 1,5,13,29… \*\* > > 1. Each number is the sum of the preceding number and a successive product of 4: 1+4=5, 5+8=13, 13+16=29, 29+32=61. \*\* I came up with 61 also, but from a simpler formula: Each number is 3 plus the previous number doubled. 3+2_1 = 5 3+2_5 = 13 3+2_13 = 29 3+2_29 = 61 ---
**Author:** ![armedmonkey](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@armedmonkey](https://boards.straightdope.com/u/armedmonkey)\ **Post date:** [August 15, 2001, 5:56pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/7 "2001-08-15T17:56:21Z")
\*\* [/QUOTE] 2 is prime. \*\* [/QUOTE] yep, you’re right. Would have worked if FTfirefly had replaced 1 with 2. Oh well. Who gets to post the next series? ---
**Author:** ![Fiddle\_Peghead](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fiddle_peghead/32/3506_2.png) [@Fiddle\_Peghead](https://boards.straightdope.com/u/Fiddle_Peghead)\ **Post date:** [August 15, 2001, 8:24pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/8 "2001-08-15T20:24:50Z")
Even though I didn’t post the answer first, I got it without looking at those who did. Therefore, since no one has presented another sequence, I will: 7,24,58,126 ---
**Author:** ![armedmonkey](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@armedmonkey](https://boards.straightdope.com/u/armedmonkey)\ **Post date:** [August 15, 2001, 8:28pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/9 "2001-08-15T20:28:02Z")
> [@](#): > > \*Originally posted by notcynical \* > \*\*Even though I didn’t post the answer first, I got it without looking at those who did. Therefore, since no one has presented another sequence, I will: > > 7,24,58,126 \*\* Too easy: 262 Double the number and add 10 Give me a second to think up the next series. ---
**Author:** ![armedmonkey](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@armedmonkey](https://boards.straightdope.com/u/armedmonkey)\ **Post date:** [August 15, 2001, 8:36pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/10 "2001-08-15T20:36:05Z")
O.K. a wee bit harder: **2,5,24,120** ---
**Author:** ![Bill\_H](https://avatars.discourse-cdn.com/v4/letter/b/a5b964/32.png) [@Bill\_H](https://boards.straightdope.com/u/Bill_H)\ **Post date:** [August 15, 2001, 8:55pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/11 "2001-08-15T20:55:55Z")
You may find this site interesting: [http://www.research.att.com/~njas/sequences/index.html](http://www.research.att.com/~njas/sequences/index.html) ---
**Author:** ![armedmonkey](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@armedmonkey](https://boards.straightdope.com/u/armedmonkey)\ **Post date:** [August 15, 2001, 9:04pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/12 "2001-08-15T21:04:12Z")
Interesting or not, it didn’t give the answer I was looking for. The formula is much simpler than whatever the Hades “Self-complementary 2-multigraphs with loops on n nodes.” is. ---
**Author:** ![Fiddle\_Peghead](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fiddle_peghead/32/3506_2.png) [@Fiddle\_Peghead](https://boards.straightdope.com/u/Fiddle_Peghead)\ **Post date:** [August 15, 2001, 9:06pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/13 "2001-08-15T21:06:35Z")
> [@](#): > > \*Originally posted by Beeblebrox \* > \*\* > > > [@](#): > > > > \*Originally posted by notcynical \* > > \*\*Even though I didn’t post the answer first, I got it without looking at those who did. Therefore, since no one has presented another sequence, I will: > > > > 7,24,58,126 \*\* > > Too easy: 262 > > Double the number and add 10 > > Give me a second to think up the next series. \*\* Wrong. You actually add five to the number, then multiply by two. ---
**Author:** ![armedmonkey](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@armedmonkey](https://boards.straightdope.com/u/armedmonkey)\ **Post date:** [August 15, 2001, 9:10pm UTC](https://boards.straightdope.com/t/whats-the-next-number-in-this-sequence-strictly-mathematical/76411/14 "2001-08-15T21:10:52Z")
> [@](#): > > \*Originally posted by notcynical \* > Wrong. You actually add five to the number, then multiply by two. \*\* That’s a joke right? I’m a little slow today. 2(X + 5) = 2X + 10