|
%I #7 Apr 04 2020 10:33:05
%S 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,2,1,1,1,2,1,1,1,2,1,1,1,2,1,1,
%T 1,3,1,1,1,2,1,2,1,2,1,1,1,3,1,1,1,2,1,2,1,2,1,1,1,3,1,1,1,3,1,2,1,2,
%U 1,1,1,4,1,1,1,2,1,2,1,3,2,1,1,3,1,1,1,3,1,3,1,2,1,1,1,4,1,1,2,3
%N Number of nonprime divisors of n that are <= sqrt(n).
%F G.f.: Sum_{k>=1} x^(A018252(k)^2) / (1 - x^A018252(k)).
%t Table[DivisorSum[n, 1 &, # <= Sqrt[n] && !PrimeQ[#] &], {n, 1, 100}]
%t nmax = 100; CoefficientList[Series[Sum[Boole[!PrimeQ[k]] x^(k^2)/(1 - x^k), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
%o (PARI) a(n) = sumdiv(n, d, (d^2<=n) && !isprime(d)); \\ _Michel Marcus_, Apr 03 2020
%Y Cf. A018252, A033273, A038548, A063962, A069288, A069291, A333749, A333750, A333751.
%K nonn
%O 1,16
%A _Ilya Gutkovskiy_, Apr 03 2020
|
