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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: A302300 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 October 19 13:01 EDT 2019. Contains 328222 sequences. (Running on oeis4.)