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 A013589 a(n+1) = a(n)*(a(n)+1)/2. 8
 4, 10, 55, 1540, 1186570, 703974775735, 247790242435923759782980, 30700002123226936025189367747945843590228731690, 471245065183069190019624521318729501785547966685566656416776916445985874756815447988119493895 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 0..11 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 * A225543 A002290 A336997 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

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Last modified December 9 23:05 EST 2022. Contains 358710 sequences. (Running on oeis4.)