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 A116073 Sum of the divisors of n that are not divisible by 5. 15
 1, 3, 4, 7, 1, 12, 8, 15, 13, 3, 12, 28, 14, 24, 4, 31, 18, 39, 20, 7, 32, 36, 24, 60, 1, 42, 40, 56, 30, 12, 32, 63, 48, 54, 8, 91, 38, 60, 56, 15, 42, 96, 44, 84, 13, 72, 48, 124, 57, 3, 72, 98, 54, 120, 12, 120, 80, 90, 60, 28, 62, 96, 104, 127, 14, 144, 68, 126, 96, 24 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES B. C. Berndt, Ramanujan's Notebooks Part III, Springer-Verlag, see p. 463 Entry 4(i). LINKS Seiichi Manyama, Table of n, a(n) for n = 1..10000 FORMULA a(n) is multiplicative with a(5^e) = 1, a(p^e) = (p^(e+1)-1)/(p-1) otherwise. G.f.: Sum_{k>0} k*x^k/(1-x^k) - 5*k*x^(5*k)/(1-x^(5*k)). L.g.f.: log(Product_{k>=1} (1 - x^(5*k))/(1 - x^k)) = Sum_{n>=1} a(n)*x^n/n. - Ilya Gutkovskiy, Mar 14 2018 MATHEMATICA f[p_, e_] := If[p == 5, 1, (p^(e+1)-1)/(p-1)]; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Sep 17 2020 *) PROG (PARI) a(n) = if(n<1, 0, sumdiv(n, d, (d%5>0)*d)) CROSSREFS Cf. A028887(n) = 6*a(n) if n>0. Cf. A145466. Cf. A035207 (number of divisors of n that are not divisible by 5). Sequence in context: A093087 A130893 A072079 * A166043 A294896 A021292 Adjacent sequences:  A116070 A116071 A116072 * A116074 A116075 A116076 KEYWORD nonn,mult AUTHOR Michael Somos, Feb 04 2006 STATUS approved

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Last modified July 31 02:33 EDT 2021. Contains 346367 sequences. (Running on oeis4.)