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%I #9 Dec 02 2020 03:19:08
%S 0,1,1,1,1,5,1,5,1,5,1,14,1,5,10,5,1,14,1,21,10,5,1,30,1,5,10,21,1,39,
%T 1,21,10,5,26,30,1,5,10,46,1,50,1,21,35,5,1,66,1,30,10,21,1,50,26,70,
%U 10,5,1,91,1,5,59,21,26,50,1,21,10,79,1,130,1,5,35,21,50,50,1,110
%N G.f.: Sum_{k>=1} k^2 * x^(k*(k + 1)) / (1 - x^k).
%C Sum of squares of divisors of n that are smaller than sqrt(n).
%H <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>
%t nmax = 80; CoefficientList[Series[Sum[k^2 x^(k (k + 1))/(1 - x^k), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
%t Table[DivisorSum[n, #^2 &, # < Sqrt[n] &], {n, 80}]
%o (PARI) a(n) = sumdiv(n, d, if (d^2 < n, d^2)); \\ _Michel Marcus_, Dec 02 2020
%Y Cf. A001157, A056924, A067558, A070039, A095118, A339354.
%K nonn
%O 1,6
%A _Ilya Gutkovskiy_, Dec 01 2020
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