A364420 - OEIS

%I #5 Jul 25 2023 09:18:25

%S 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,

%T 0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,

%U 0,0,0,1,0,0,0,1,0,0,0,1,1,0,0,1,0,0,0,1,0,1,0,1,0,0,0,1,0,0,1,1,0,0,0,1,0,0,0,2

%N Number of divisors of n of the form 5*k+4 that are at most sqrt(n).

%F G.f.: Sum_{k>=0} x^(5*k+4)^2 / (1 - x^(5*k+4)).

%t Table[Count[Divisors[n], _?(# <= Sqrt[n] && MemberQ[{4}, Mod[#, 5]] &)], {n, 108}]

%t nmax = 108; CoefficientList[Series[Sum[x^(5 k + 4)^2/(1 - x^(5 k + 4)), {k, 0, nmax}], {x, 0, nmax}], x] // Rest

%Y Cf. A001899, A038548, A364388, A364389, A364419.

%K nonn

%O 1,108

%A _Ilya Gutkovskiy_, Jul 23 2023