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%I #47 Jan 28 2024 09:03:22
%S 3,6,8,12,12,64,12,48,20,48,12,256,24,48,128,192,12,640,6,384,256,288,
%T 6,2048,96,192,96,768,96,16384,24,6144,128,192,384,5120,24,24,128,
%U 6144,48,49152,48,4608,1280,192,12,16384,48,3072,512,1536,48,12288,768
%N Number of divisors of 10^n-1 (999...999 with n digits).
%H <a href="/A070528/b070528.txt">Table of n, a(n) for n = 1..352</a>
%F a(n) = A000005(A002283(n)).
%F a(n) = Sum_{d|n} A059892(d).
%F a(n) = A070529(n)*(A007949(n)+3)/(A007949(n)+1).
%e a(7)=12 since the divisors of 9999999 are 1, 3, 9, 239, 717, 2151, 4649, 13947, 41841, 1111111, 3333333, 9999999.
%t DivisorSigma[0,#]&/@(10^Range[60]-1) (* _Harvey P. Dale_, Jan 14 2011 *)
%t Table[DivisorSigma[0, 10^n - 1], {n, 60}] (* _T. D. Noe_, Aug 18 2011 *)
%o (PARI) a(n) = numdiv(10^n - 1); \\ _Michel Marcus_, Sep 08 2015
%Y Cf. A004023 (indices of 6's).
%Y Cf. A018282, A018766, A027894, A027893, A027892, A027891, A027890, A027889, A027895.
%Y Cf. A046801, A005422, A102347, A046053, A057951, A007138, A003060, A059892, A085035.
%K base,nonn
%O 1,1
%A _Henry Bottomley_, May 02 2002
%E Terms to a(280) in b-file from _Hans Havermann_, Aug 19 2011
%E a(281)-a(322) in b-file from _Ray Chandler_, Apr 22 2017
%E a(323)-a(352) in b-file from _Max Alekseyev_, May 04 2022
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