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A364388
Number of divisors of n of the form 5*k+1 that are at most sqrt(n).
4
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
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
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jul 21 2023
STATUS
approved