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A050548 Iterated triangular numbers. 9
7, 28, 406, 82621, 3413156131, 5824817388998022646, 16964248807586870937449001943463431981, 143892868802856286225154411591351342616163027795335641150249224655238508171 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(8) has 149 digits. - Harvey P. Dale, May 08 2011

LINKS

T. D. Noe, Table of n, a(n) for n = 0..10

FORMULA

a(n) = binomial(a(n-1)+1, 2), a(0)=7.

a(n) ~ 2 * c^(2^n), where c = 3.77579046114281148578572146955902030830005575599864345238... . - Vaclav Kotesovec, Dec 17 2014

MATHEMATICA

NestList[Binomial[#+1, 2]&, 7, 10] (* Harvey P. Dale, May 08 2011 *)

t = {7}; Do[AppendTo[t, t[[-1]]*(1 + t[[-1]])/2], {9}] (* T. D. Noe, Mar 03 2014 *)

PROG

(PARI) a(n)=my(k=7); for(i=1, n, k=binomial(k+1, 2)); k \\ Charles R Greathouse IV, Mar 03 2014

(Haskell)

a050548 n = a050548_list !! n

a050548_list = iterate a000217 7

CROSSREFS

Cf. A000217, A007501, A013589.

Cf. A050542, A050536, A050909.

Sequence in context: A244300 A203209 A193288 * A261845 A181942 A140447

Adjacent sequences:  A050545 A050546 A050547 * A050549 A050550 A050551

KEYWORD

easy,nice,nonn

AUTHOR

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

EXTENSIONS

a(7) provided by Harvey P. Dale, May 08 2011

STATUS

approved

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Last modified February 19 09:09 EST 2018. Contains 299330 sequences. (Running on oeis4.)