

A120357


a(n) is the smallest prime p such that 2^p1 (a Mersenne number) contains 10^n or more decimal digits.


1



2, 31, 331, 3319, 33223, 332191, 3321937, 33219281, 332192831, 3321928097, 33219280951, 332192809589, 3321928094941, 33219280948907, 332192809488739, 3321928094887411, 33219280948873687, 332192809488736253
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OFFSET

0,1


COMMENTS

For n>0 almost all digits of a(n) from the left are equal to the first terms of the expansion Log[10]/Log[2] = {3, 3, 2, 1, 9, 2, 8, 0, 9, 4, 8, 8, 7, 3, 6, 2, 3, 4, 7, 8, 7, 0, 3, 1, 9, 4, 2, 9, 4, 8, 9, 3, 9, ...} = A020862(n).  Alexander Adamchuk, Jan 16 2007


LINKS

Author?, GIMPS [Broken link?]


EXAMPLE

E.g. a(7)=33219281 because 2^332192811 is the smallest Mersenne number that contains 10^7 (ten million) or more decimal digits.


CROSSREFS

Cf. A020862 = decimal expansion of log(10)/log(2).


KEYWORD

base,nonn


AUTHOR



EXTENSIONS



STATUS

approved



