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 A050548 #23 Sep 29 2023 18:59:20
%S A050548 7,28,406,82621,3413156131,5824817388998022646,
%T A050548 16964248807586870937449001943463431981,
%U A050548 143892868802856286225154411591351342616163027795335641150249224655238508171
%N A050548 Iterated triangular numbers with seed 7.
%C A050548 a(8) has 149 digits. - _Harvey P. Dale_, May 08 2011
%H A050548 T. D. Noe, <a href="/A050548/b050548.txt">Table of n, a(n) for n = 0..10</a>
%F A050548 a(n) = binomial(a(n-1)+1, 2), a(0)=7.
%F A050548 a(n) ~ 2 * c^(2^n), where c = 3.77579046114281148578572146955902030830005575599864345238... . - _Vaclav Kotesovec_, Dec 17 2014
%t A050548 NestList[Binomial[#+1,2]&,7,10] (* _Harvey P. Dale_, May 08 2011 *)
%t A050548 t = {7}; Do[AppendTo[t, t[[-1]]*(1 + t[[-1]])/2], {9}] (* _T. D. Noe_, Mar 03 2014 *)
%o A050548 (PARI) a(n)=my(k=7); for(i=1,n,k=binomial(k+1,2)); k \\ _Charles R Greathouse IV_, Mar 03 2014
%o A050548 (Haskell)
%o A050548 a050548 n = a050548_list !! n
%o A050548 a050548_list = iterate a000217 7
%o A050548 (Python)
%o A050548 from itertools import accumulate
%o A050548 def f(an, _): return an*(an+1)//2
%o A050548 print(list(accumulate([7]*11, f))) # _Michael S. Branicky_, Jul 28 2021
%Y A050548 Cf. A000217, A007501, A013589.
%Y A050548 Cf. A050542, A050536, A050909.
%K A050548 nonn,easy,nice
%O A050548 0,1
%A A050548 Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Dec 29 1999
%E A050548 a(7) provided by _Harvey P. Dale_, May 08 2011