The On-Line Encyclopedia of Integer Sequences (OEIS)

A083915 revision #6

A083915

Number of divisors of n that are congruent to 5 modulo 10.

0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 2, 0, 0, 0, 0, 1, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 1, 0, 0, 0, 0, 3, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 4, 0, 0, 0, 0, 1, 0, 0, 0, 0, 2, 0, 0, 0, 0, 3, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 4

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OFFSET

1,15

LINKS

Table of n, a(n) for n=1..105.

FORMULA

a(n) = A000005(n) - A083910(n) - A083911(n) - A083912(n) - A083913(n) - A083914(n) - A083916(n) - A083917(n) - A083918(n) - A083919(n).

G.f.: Sum_{k>=1} x^(5*k)/(1 - x^(10*k)). - Ilya Gutkovskiy, Sep 11 2019

MATHEMATICA

Table[Count[Divisors[n], _?(Mod[#, 10]==5&)], {n, 120}] (* Harvey P. Dale, Jan 26 2018 *)

CROSSREFS

Cf. A010879, A000005, A001227.