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URL: https://oeis.org/A051572

⇱ A051572 - OEIS

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A051572
a(1) = 5, a(n) = sigma(a(n-1)).
6
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
OFFSET
1,1
LINKS
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 and 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
KEYWORD
easy,nonn
AUTHOR
STATUS
approved