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A102146 a(n) = sigma(10^n - 1), where sigma(n) is the sum of positive divisors of n. 1

%I

%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 Ray Chandler, <a href="/A102146/b102146.txt">Table of n, a(n) for n = 1..322</a>

%H C. Caldwell, <a href="http://primes.utm.edu/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, A002283, A070528.

%K nonn

%O 1,1

%A Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Feb 14 2005

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Last modified August 21 22:32 EDT 2019. Contains 326169 sequences. (Running on oeis4.)