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%I #15 Jan 05 2024 17:11:54
%S 13,156,1520,15912,148512,2042880,14508000,162493344,1534205464,
%T 16203253248,144451398000,2063316971520,14903272088640,
%U 158269280832000,1614847741624320,17205180696931968,144444514193267496
%N a(n) = sigma(10^n - 1), where sigma(n) is the sum of positive divisors of n.
%H Max Alekseyev, <a href="/A102146/b102146.txt">Table of n, a(n) for n = 1..352</a> (terms 1..322 from Ray Chandler)
%H C. Caldwell, <a href="https://t5k.org/glossary/page.php?sort=SigmaFunction">Sigma function</a>.
%F a(n) = A000203(A002283(n)). - _Ray Chandler_, Apr 22 2017
%t DivisorSigma[1,10^Range[20]-1] (* _Harvey P. Dale_, Jan 05 2012 *)
%o (PARI) a(n) = sigma(10^n-1); \\ _Michel Marcus_, Apr 22 2017
%Y Cf. A000203, A001270, A002283, A003020, A005422, A046053, A046107, A046412, A046415, A046416, A046417, A046418, A046419, A046420, A057951, A059892, A061075, A070528, A070529, A081317, A081318, A085035, A095370, A095413, A095414, A095417, A095418, A102347, A102380, A112505, A147556, A295503, A366669.
%K nonn
%O 1,1
%A Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Feb 14 2005