Post #1783599

2026-04-27 11:56 UTC

I&#39;ve come up with another sequence that I can&#39;t believe isn&#39;t in the #OEIS (#ICBINIOEIS)! 1, 3, 7, 11, 16, 25, ... Can you guess the next term? Can you guess the general rule? I haven&#39;t done one of these for a while, but the usual rules apply: * You can ask for hints. Say if you want a big, medium or small hint. * Put any guesses under a content warning. * If nobody correctly guesses it, I&#39;ll post the answer in a week or so.

Replies (3)

@markgritter@mathstodon.xyz 2026-04-27 18:05

@christianp the differences 2,4,4,5,9 do appear multiple times. :) To me these seem like they are close to the triangular numbers. a(1) = 1 = T_1 a(2) = 3 = T_2 a(3) = 7 = T_3 + T_1 a(4) = 11 = T_4 + T_1 a(5) = 16 = T_5 + T_1 a(6) = 25 = T_6 + T_2 + T_1 Guess is a(7) = 32 = T_7 + T_2 + T_1 a(8) = 40 = T_8 + T_2 + T_1 a(9) = 55 = T_9 + T_3 + T_2 + T_1 ? But I am also guessing that is just coincidence. I spent too long looking at https://oeis.org/A327629 to see if its partial sums had some reasonable interpretation.

Open ##2021684
@0x10f@tech.lgbt 2026-04-27 19:42

@christianp I only found out it resembles this sequence you've contributed to: https://oeis.org/A330070 Edit: word choice

Open ##2021686
@christianp@mathstodon.xyz 2026-05-06 05:02

Lay down number bars 1, 2, 3, ... Put the bar as far to the left as you can, as high as you can: if you can stack on top of previous bars, then do so. The first 25 bars look like the attached image. The sequence is the lengths of the leftmost bar on each row. Next two terms are 32, 40. Now in the #OEIS: https://oeis.org/A395531

Open ##2658771