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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-François 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.)