

A050548


Iterated triangular numbers.


9



7, 28, 406, 82621, 3413156131, 5824817388998022646, 16964248807586870937449001943463431981, 143892868802856286225154411591351342616163027795335641150249224655238508171
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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(n1)+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.uniduesseldorf.de), Dec 29 1999


EXTENSIONS

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


STATUS

approved



