A050536 Iterated triangular numbers with seed 8.

8, 36, 666, 222111, 24666759216, 304224505122393846936, 46276274758482720006792605816457695217516, 1070746802761292462947634762387664148872006333922794021004562705432032738124213886

Offset: 0

Author

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

Keywords

• easy
• nice
• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 0..10

Crossrefs

Cf. A000217.

Cf. A007501, A013589, A050542, A050548, A050909.

Programs

Haskell

a050536 n = a050536_list !! n
a050536_list = iterate a000217 8  -- Reinhard Zumkeller, Apr 10 2014

Mathematica

NestList[Binomial[#+1,2]&,8,7] (* Harvey P. Dale, Jan 22 2016 *)

PARI

a(n)=if(n==0,8,(a(n-1))*(a(n-1)+1)/2) \\ Edward Jiang, Sep 07 2014

Formula

a(n) = binomial(a(n-1)+1, 2), a(0)=8.

a(n) ~ 2 * c^(2^n), where c = 4.2726038862497240421168669075178596377687659229240586312... . - Vaclav Kotesovec, Dec 17 2014

Extensions

One more term (a(7)) from Harvey P. Dale, Jan 22 2016