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A051572 a(1) = 5, a(n) = sigma(a(n-1)). 5
5, 6, 12, 28, 56, 120, 360, 1170, 3276, 10192, 24738, 61440, 196584, 491520, 1572840, 5433480, 20180160, 94859856, 355532800, 1040179456, 2143289344, 4966055344, 10092086208, 31800637440, 137371852800, 641012414823 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..523

G. L. Cohen and H. J. J. te Riele, Iterating the sum-of-divisors function, Experimental Mathematics, 5 (1996), pp. 91-100.

Graeme L. Cohen, Herman J. J. te Riele, Iterating the Sum-of-Divisors Function, Experimental Mathematics, Vol. 5 (1996), No. 2, pp. 91-100.

MATHEMATICA

NestList[Plus@@Divisors[#] &, 5, 25] (* Alonso del Arte, Apr 28 2011 *)

PROG

(PARI) a=[5]; for(i=2, 10, a=concat(a, sigma(a[#a]))); a \\ Charles R Greathouse IV, Oct 03 2011

(Python)

from itertools import accumulate, repeat # requires Python 3.2 or higher

from sympy import divisor_sigma

A051572_list = list(accumulate(repeat(5, 100), lambda x, _: divisor_sigma(x)))

# Chai Wah Wu, May 02 2015

CROSSREFS

Cf. A000203, A007497, A257348.

Sequence in context: A126593 A173074 A099473 * A047436 A061437 A067245

Adjacent sequences:  A051569 A051570 A051571 * A051573 A051574 A051575

KEYWORD

easy,nonn

AUTHOR

Judson D. Neer (judson(AT)poboxes.com)

STATUS

approved

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Last modified November 19 03:53 EST 2017. Contains 294912 sequences.