A013589 a(n+1) = a(n)*(a(n)+1)/2.

4, 10, 55, 1540, 1186570, 703974775735, 247790242435923759782980, 30700002123226936025189367747945843590228731690, 471245065183069190019624521318729501785547966685566656416776916445985874756815447988119493895

Offset

0,1

Links

Reinhard Zumkeller, Table of n, a(n) for n = 0..11

Index entries for sequences of form a(n+1)=a(n)^2 + ...

Formula

a(n) ~ 2 * c^(2^n), where c = 2.29524458756644851072790131811443639562180382439442714497... . - Vaclav Kotesovec, Dec 17 2014

Maple

f := proc(n) options remember; if n = 0 then 4 else 1/2*f(n-1)*(f(n-1)+1) fi end

Mathematica

a=4; lst={a}; Do[b=(a+1)*a/2; AppendTo[lst, b]; a=b, {n, 1, 9}]; lst (* Vladimir Joseph Stephan Orlovsky, Mar 16 2010 *)
NestList[# (#+1)/2&, 4, 10] (* Harvey P. Dale, Sep 20 2012 *)

Prog

(Haskell)
a013589 n = a013589_list !! n
a013589_list = iterate a000217 4  -- Reinhard Zumkeller, Apr 10 2014

Crossrefs

Cf. A000217, A007501, A050542, A050536, A050548, A050909.

Cf. A086714.

Sequence in context: A096423 A276130 A263044 * A367430 A225543 A002290

Adjacent sequences: A013586 A013587 A013588 * A013590 A013591 A013592

Keyword

nonn

Author

Carl Bellinger (carlb(AT)ctron.com)

Extensions

One more term from Vladimir Joseph Stephan Orlovsky, Mar 16 2010

Status

approved