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 A099968 #15 Aug 03 2021 19:05:00
%S A099968 1,2,3,6,14,31,78,235,665,1926,5886,21832,75333,266377,933842,3422282,
%T A099968 14954936,61055379,254751651,1054728818,4378056288,18699691530,
%U A099968 94021272519,443332334411,2132051480643,10181045388314,48729093879838
%N A099968 Second column of triangle in A099964.
%H A099968 Reinhard Zumkeller, <a href="/A099968/b099968.txt">Table of n, a(n) for n = 1..750</a>
%p A099968 with(linalg):rev:=proc(a) local n, p; n:=vectdim(a): p:=i->a[n+1-i]: vector(n,p) end: ps:=proc(a) local n, q; n:=vectdim(a): q:=i->sum(a[j],j=1..i): vector(n,q) end: pss:=proc(a) local n, q; n:=vectdim(a): q:=proc(i) if i<=n then sum(a[j],j=1..i) else sum(a[j],j=1..n) fi end: vector(n+1,q) end: tr:={seq(n*(n+1)/2,n=1..30)}: R[0]:=vector(1,1): for n from 1 to 30 do if member(n,tr)=false then R[n]:=ps(rev(R[n-1])) else R[n]:=pss(rev(R[n-1])) fi od: seq(R[n][2],n=1..30); # _Emeric Deutsch_, Nov 16 2004
%o A099968 (Haskell)
%o A099968 a099968 = flip a099964 1 -- _Reinhard Zumkeller_, May 02 2012
%Y A099968 Cf. A099964, A099965, A099966.
%K A099968 nonn,easy
%O A099968 1,2
%A A099968 _N. J. A. Sloane_, Nov 13 2004
%E A099968 More terms from _Emeric Deutsch_, Nov 16 2004
%E A099968 Offset corrected by _Reinhard Zumkeller_, May 02 2012