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%I #14 Dec 07 2019 17:22:50
%S 1,1,2,3,4,4,6,6,7,9,10,12,13,13,15,16,18,19,21,22,22,24,25,27,30,31,
%T 32,33,33,35,39,40,42,42,45,46,48,50,51,53,54,55,58,59,60,60,64,68,69,
%U 69,71,72,73,76,78,80,81,82,84,85,86,89,93,94,95,96,100
%N Number of digits in n-th Mersenne number.
%F a(n) = floor(log_10(A001348(n))) + 1.
%e For n = 5, the fifth prime number is 11, so 2^11 - 1 = 2047 is the fifth Mersenne number, which has 4 digits, so a(5) = 4.
%o (PARI) a227683(n) = floor(log(2^prime(n)-1)/log(10)) + 1 \\ _Michael B. Porter_, Jul 20 2013
%Y Cf. A000040, A001348.
%K nonn,base
%O 1,3
%A _Olivier de Mouzon_, Jul 19 2013
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