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%I #31 Jan 02 2017 02:38:24
%S 0,1,66,1577,18218,135550,738236,3207785,11714718,37347144,106499470,
%T 277489886,668981686,1512360404,3228797252,6570019945,12793050456,
%U 24001960051,43483452090,76485144056,130752372320,218220937122,355664809556,568293832670,889969136158
%N a(n) = Sum_{k=1..n-1} sigma_5(k)*sigma_5(n-k).
%C In 1916, Ramanujan found the following identity. tau(n) = sigma_11(n) - 691/756 * (sigma_11(n) - sigma_5(n) + 252 * a(n)). This implies tau(n) == sigma_11(n) mod 691.
%H Seiichi Manyama, <a href="/A279889/b279889.txt">Table of n, a(n) for n = 1..1000</a>
%F A027860(n) = (sigma_11(n) - sigma_5(n) + 252*a(n))/756.
%o (PARI) a(n) = sum(k=1, n-1, sigma(k, 5)*sigma(n-k, 5)) \\ _Felix Fröhlich_, Jan 01 2017
%Y Cf. Sum_{k=1..n-1} sigma_m(k)*sigma_m(n-k): A087115 (m=3), this sequence (m=5).
%Y Cf. A000594, A001160, A013959, A027860.
%K nonn
%O 1,3
%A _Seiichi Manyama_, Dec 22 2016