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A279888 a(n) = Sum_{k=1..n-1} sigma_3(k)*sigma_5(n-k). 3

%I #21 Dec 24 2016 02:04:55

%S 0,1,42,569,4250,22006,88004,293369,845358,2186376,5145646,11282966,

%T 23143198,45179324,83905292,150271993,258816840,433786483,704268402,

%U 1119633944,1733618768,2640037170,3931060364,5777392406,8325691750,11873200964,16643954724,23133008124

%N a(n) = Sum_{k=1..n-1} sigma_3(k)*sigma_5(n-k).

%D J.-P. Serre, A Course in Arithmetic, Springer-Verlag, 1973, Chap. VII, Section 4.

%H Seiichi Manyama, <a href="/A279888/b279888.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = (11*sigma_9(n)-21*sigma_5(n)+10*sigma_3(n))/5040.

%t Table[Sum[If[k == 0, 0, DivisorSigma[3, k]] DivisorSigma[5, n - k], {k, 0, n - 1}], {n, 28}] (* _Michael De Vlieger_, Dec 22 2016 *)

%Y Cf. A001158, A001160, A013957, A279917.

%K nonn

%O 1,3

%A _Seiichi Manyama_, Dec 22 2016

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Last modified March 28 17:25 EDT 2024. Contains 371254 sequences. (Running on oeis4.)