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A050909 Iterated triangular numbers. 10
9, 45, 1035, 536130, 143717956515, 10327425512495574450870, 53327858858072239299138189326373798809103885 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

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

FORMULA

a(n) = binomial(a(n-1)+1, 2), a(0)=9.

a(n) ~ 2 * c^(2^n), where c = 4.770128350983276481977311510917830191429308415174884373259... . - Vaclav Kotesovec, Dec 17 2014

MATHEMATICA

NestList[Binomial[#+1, 2]&, 9, 10] (* Harvey P. Dale, Oct 12 2011 *)

PROG

(Haskell)

a050909 n = a050909_list !! n

a050909_list = iterate a000217 9  -- Reinhard Zumkeller, Apr 10 2014

(PARI) a(n)=if(n, binomial(a(n-1)+1, 2), 9) \\ Charles R Greathouse IV, Feb 07 2017

CROSSREFS

Cf. A000217, A007501, A013589, A050542, A050536, A050548.

Sequence in context: A244302 A177742 A261847 * A230062 A224851 A042003

Adjacent sequences:  A050906 A050907 A050908 * A050910 A050911 A050912

KEYWORD

easy,nice,nonn

AUTHOR

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

STATUS

approved

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Last modified February 17 23:47 EST 2018. Contains 299297 sequences. (Running on oeis4.)