This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A051572 #28 Aug 06 2024 07:03:15 %S A051572 5,6,12,28,56,120,360,1170,3276,10192,24738,61440,196584,491520, %T A051572 1572840,5433480,20180160,94859856,355532800,1040179456,2143289344, %U A051572 4966055344,10092086208,31800637440,137371852800,641012414823 %N A051572 a(1) = 5, a(n) = sigma(a(n-1)). %H A051572 N. J. A. Sloane, <a href="/A051572/b051572.txt">Table of n, a(n) for n = 1..523</a> %H A051572 G. L. Cohen and H. J. J. te Riele, <a href="http://projecteuclid.org/euclid.em/1047565640">Iterating the sum-of-divisors function</a>, Experimental Mathematics, 5 (1996), pp. 91-100. %H A051572 Graeme L. Cohen and Herman J. J. te Riele, <a href="https://citeseerx.ist.psu.edu/pdf/1a17663b1c58f07a3b9164d2c0d9e7d57d6464be">Iterating the Sum-of-Divisors Function</a>, Experimental Mathematics, Vol. 5 (1996), No. 2, pp. 91-100. %t A051572 NestList[Plus@@Divisors[#] &, 5, 25] (* _Alonso del Arte_, Apr 28 2011 *) %o A051572 (PARI) a=[5];for(i=2,10,a=concat(a,sigma(a[#a]))); a \\ _Charles R Greathouse IV_, Oct 03 2011 %o A051572 (Python) %o A051572 from itertools import accumulate, repeat # requires Python 3.2 or higher %o A051572 from sympy import divisor_sigma %o A051572 A051572_list = list(accumulate(repeat(5,100), lambda x, _: divisor_sigma(x))) %o A051572 # _Chai Wah Wu_, May 02 2015 %Y A051572 Cf. A000203, A007497, A257348. %K A051572 easy,nonn %O A051572 1,1 %A A051572 _Judson Neer_