%I #8 Jul 17 2020 22:34:41
%S 2,5,26,850,943950,1318281510000,2755017380686402917800000,
%T 10751241448828145947377163154256928532205365443200,
%U 186653497320711305248493130820948403307540799528422902350199946673943964748877201760000000000000000
%N a(n) = sigma_2(a(n-1)): sum of squares of divisors of a(n-1) with a(1)=2.
%C Are all following terms divisible by 10?
%H Robert Gerbicz, <a href="/A138613/b138613.txt">Table of n, a(n) for n = 1..12</a>
%F a(n>=1) = sigma_2(a(n-1)) = A001157(a(n-1)), a(1)=2.
%e a(1)=2, divisors of 2: {1,2}, hence a(2)=1^2+2^2=5;
%e a(2)=5, divisors of 5: {1,5}, hence a(3)=1^2+5^2=26;
%e a(3)=26, divisors of 26: {1,2,13,26}, hence a(4)=1^2+2^2+13^2+26^2=850.
%t NestList[DivisorSigma[2, # ]&,2,9]
%Y Cf. A001157, A033766, A079488.
%K nonn
%O 1,1
%A _Zak Seidov_, May 14 2008