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A178144 Sum of divisors d of n which are d=2, 3 or 5. 3
0, 2, 3, 2, 5, 5, 0, 2, 3, 7, 0, 5, 0, 2, 8, 2, 0, 5, 0, 7, 3, 2, 0, 5, 5, 2, 3, 2, 0, 10, 0, 2, 3, 2, 5, 5, 0, 2, 3, 7, 0, 5, 0, 2, 8, 2, 0, 5, 0, 7, 3, 2, 0, 5, 5, 2, 3, 2, 0, 10, 0, 2, 3, 2, 5, 5, 0, 2, 3, 7, 0, 5, 0, 2, 8, 2, 0, 5, 0, 7, 3, 2, 0, 5, 5, 2, 3, 2, 0, 10, 0, 2, 3, 2, 5, 5, 0, 2, 3, 7, 0, 5, 0, 2, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The sequence is periodic with period length 30.

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..10000

V. Shevelev, A recursion for divisor function over divisors belonging to a prescribed finite sequence of positive integers and a solution of the Lahiri problem for divisor function sigma_x(n), arXiv:0903.1743 [math.NT], 2009.

Index entries for linear recurrences with constant coefficients, signature (-2,-2,-1,0,1,2,2,1).

FORMULA

a(n) = -2*a(n-1) -2*a(n-2) -a(n-3) +a(n-5) +2*a(n-6) +2*a(n-7) +a(n-8). R. J. Mathar, Jul 23 2012

G.f.: ( -x*(2+7*x+12*x^2+17*x^3+22*x^4+10*x^6+20*x^5) ) / ( (x-1)*(1+x)*(1+x+x^2)*(x^4+x^3+x^2+x+1) ). - R. J. Mathar, Jul 23 2012

MAPLE

A178144 := proc(n)

    local a;

    a := 0 ;

    for d in {2, 3, 5} do

        if (n mod d) = 0 then

            a := a+d ;

        end if;

    end do:

    a ;

end proc: # R. J. Mathar, Jul 23 2012

MATHEMATICA

a[n_] := DivisorSum[n, Boole[MatchQ[#, 2|3|5]]*#&];

Array[a, 105] (* Jean-Fran├žois Alcover, Nov 24 2017 *)

PROG

(PARI) a(n) = sumdiv(n, d, if ((d==2) || (d==3) || (d==5), d)); \\ Michel Marcus, Nov 24 2017

CROSSREFS

Cf. A000203, A008472, A178143, A171182, A178142.

Sequence in context: A075365 A268466 A075274 * A135737 A125179 A141821

Adjacent sequences:  A178141 A178142 A178143 * A178145 A178146 A178147

KEYWORD

nonn,easy

AUTHOR

Vladimir Shevelev, May 21 2010

STATUS

approved

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Last modified February 21 01:29 EST 2019. Contains 320364 sequences. (Running on oeis4.)