A050542 - OEIS

%I #20 Sep 29 2023 18:58:55

%S 5,15,120,7260,26357430,347357071281165,60328467484514345085777519195,

%T 1819761994515052295911016533077539330911500847167185483610

%N Iterated triangular numbers with seed 5.

%H Reinhard Zumkeller, <a href="/A050542/b050542.txt">Table of n, a(n) for n = 0..11</a>

%F a(n) = binomial(a(n-1)+1, 2), a(0)=5.

%F a(n) ~ 2 * c^(2^n), where c = 2.786070277619247476352890606543375642991890742669788965024... . - _Vaclav Kotesovec_, Dec 17 2014

%t a=5;lst={a};Do[b=(a+1)*a/2;AppendTo[lst,b];a=b,{n,1,9}];lst ( _Vladimir Joseph Stephan Orlovsky_, Mar 16 2010 *)

%t NestList[Binomial[#+1,2]&,5,9] (* _Harvey P. Dale_, Sep 24 2011 *)

%o (Haskell)

%o a050542 n = a050542_list !! n

%o a050542_list = iterate a000217 5  -- _Reinhard Zumkeller_, Apr 10 2014

%o (PARI) a(n)=if(n, binomial(a(n-1)+1, 2), 5) \\ _Charles R Greathouse IV_, Feb 08 2017

%Y Cf. A000217, A007501, A013589, A050536, A050548, A050909.

%K easy,nice,nonn

%O 0,1

%A Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Dec 29 1999