A083916 - OEIS

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A083916

Number of divisors of n that are congruent to 6 modulo 10.

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

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OFFSET

1,36

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

R. A. Smith and M. V. Subbarao, The average number of divisors in an arithmetic progression, Canadian Mathematical Bulletin, Vol. 24, No. 1 (1981), pp. 37-41.

FORMULA

a(n) = A000005(n) - A083910(n) - A083911(n) - A083912(n) - A083913(n) - A083914(n) - A083915(n) - A083917(n) - A083918(n) - A083919(n).

G.f.: Sum_{k>=1} x^(6*k)/(1 - x^(10*k)). - Ilya Gutkovskiy, Sep 11 2019

Sum_{k=1..n} a(k) = n*log(n)/10 + c*n + O(n^(1/3)*log(n)), where c = gamma(6,10) - (1 - gamma)/10 = -0.118475..., gamma(6,10) = -(psi(3/5) + log(10))/10 is a generalized Euler constant, and gamma is Euler's constant (A001620) (Smith and Subbarao, 1981). - Amiram Eldar, Dec 30 2023

MATHEMATICA

Table[Count[Divisors[n], _?(Mod[#, 10]==6&)], {n, 110}] (* Harvey P. Dale, Oct 16 2013 *)

a[n_] := DivisorSum[n, 1 &, Mod[#, 10] == 6 &]; Array[a, 100] (* Amiram Eldar, Dec 30 2023 *)

PROG

(PARI) a(n) = sumdiv(n, d, d % 10 == 6); \\ Amiram Eldar, Dec 30 2023

CROSSREFS

Cf. A000005, A001227, A010879.

Cf. A001620, A002392, A200137 (psi(3/5)).

Cf. A083910, A083911, A083912, A083913, A083914, A083915, A083917, A083918, A083919.

Sequence in context: A010105 A341618 A337690 * A083893 A187097 A094428

Adjacent sequences: A083913 A083914 A083915 * A083917 A083918 A083919

KEYWORD

nonn,easy

AUTHOR

Reinhard Zumkeller, May 08 2003

STATUS

approved