1,1

Table of n, a(n) for n=1..68.

a(1) = number of digits of 1996 = 4.

a(2) = number of digits of 19984 = 5.

a(3) = number of digits of 1999936 = 7 and

a(68)=7235, because smallest prime of the form 5^(2*68-1)*10^m -1 is 5^135*10^7099-1 and 4^68(5^135*10^7099-1) has 7235 digits.

Cf. A248857.

Sequence in context: A202342 A234141 A093517 * A145018 A018910 A022936

Adjacent sequences: A248855 A248856 A248857 * A248859 A248860 A248861

nonn,base

Farideh Firoozbakht, Jan 06 2015

approved