A364388 Number of divisors of n of the form 5*k+1 that are at most sqrt(n).

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1

Offset

1,36

Links

Table of n, a(n) for n=1..100.

Formula

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

Mathematica

Table[Count[Divisors[n], _?(# <= Sqrt[n] && MemberQ[{1}, Mod[#, 5]] &)], {n, 100}]
nmax = 100; CoefficientList[Series[Sum[x^(5 k + 1)^2/(1 - x^(5 k + 1)), {k, 0, nmax}], {x, 0, nmax}], x] // Rest

Crossrefs

Cf. A001876, A038548, A364389.

Sequence in context: A318809 A304118 A319679 * A242073 A245477 A319689

Adjacent sequences: A364385 A364386 A364387 * A364389 A364390 A364391

Keyword

nonn

Author

Ilya Gutkovskiy, Jul 21 2023

Status

approved