This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A081491 #13 Feb 14 2024 12:29:12
%S A081491 1,2,3,4,6,8,9,12,15,18,19,23,27,31,35,36,41,46,51,56,61,62,68,74,80,
%T A081491 86,92,98,99,106,113,120,127,134,141,148,149,157,165,173,181,189,197,
%U A081491 205,213,214,223,232,241,250,259,268,277,286,295,296,306,316,326,336,346
%N A081491 Triangle read by rows in which the n-th row contains n terms of an arithmetic progression with a common difference of (n-1) and the first term of (n+1)-th row is 1 more than the last term of the n-th row.
%H A081491 Harvey P. Dale, <a href="/A081491/b081491.txt">Table of n, a(n) for n = 1..10000</a>
%e A081491 1; 2,3; 4,6,8; 9,12,15,18; 19,23,27,31,35; 36,41,46,51,56,61; ...
%t A081491 Table[NestList[#+n-1&,(2n^3-9n^2+19n-6)/6,n-1],{n,11}]//Flatten (* _Harvey P. Dale_, Feb 12 2024 *)
%Y A081491 Cf. A002522, A005408, A081489, A081490, A081492.
%K A081491 nonn,tabl
%O A081491 1,2
%A A081491 _Amarnath Murthy_, Mar 25 2003
%E A081491 More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 29 2003