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 A119713 #12 Nov 09 2024 00:57:02
%S A119713 0,2,7,12,21,30,39,53,67,81,95,115,135,155,175,195,222,249,276,303,
%T A119713 330,357,392,427,462,497,532,567,602,646,690,734,778,822,866,910,954,
%U A119713 1008,1062,1116,1170,1224,1278,1332,1386,1440,1505,1570,1635,1700,1765,1830
%N A119713 First differences are 2, 5, 5, 9, 9, 9, 14, 14, 14, 14, ..., that is, A000096 with m-th term repeated m times (m>=1).
%D A119713 David Pagni, Building buildings with triangular numbers, AMATYC Review (vol. 27 no. 2 spring 2006, pp. 56-65).
%F A119713 a(n) = m(12n+m(4n-m(m+2)+1)+2)/8 where m = A002024(n). - _Chai Wah Wu_, Nov 08 2024
%t A119713 a = 10; lst = {0}; s = 0; t = Flatten@ Table[ Table[n*(n + 3)/2, {n}], {n, a}]; Do[ AppendTo[lst, s = s + t[[n]]], {n, a(a+1)/2}]; lst (* _Robert G. Wilson v_, Jun 16 2006 *)
%o A119713 (Python)
%o A119713 from math import isqrt
%o A119713 def A119713(n): return (r:=(m:=isqrt(k:=n<<1))+(k>m*(m+1)))*(12*n+r*((n<<2)-r*(r+2)+1)+2)>>3 # _Chai Wah Wu_, Nov 08 2024
%Y A119713 Cf. A000096, A002024.
%K A119713 nonn
%O A119713 0,2
%A A119713 _N. J. A. Sloane_, Jun 13 2006
%E A119713 More terms from _Robert G. Wilson v_, Jun 16 2006