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