The On-Line Encyclopedia of Integer Sequences (OEIS)

A083917 revision #8

A083917

Number of divisors of n that are congruent to 7 modulo 10.

0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1

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OFFSET

1,77

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) - A083915(n) - A083916(n) - A083918(n) - A083919(n).

G.f.: Sum_{k>=1} x^(7*k)/(1 - x^(10*k)). - Ilya Gutkovskiy, Sep 11 2019

MATHEMATICA

Table[Count[Divisors[n], _?(Mod[#, 10]==7&)], {n, 110}] (* Harvey P. Dale, Sep 15 2023 *)

CROSSREFS

Cf. A010879, A000005, A001227.