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%I #20 Dec 18 2016 01:46:40
%S 1,1,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
%T 4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
%U 5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5
%N Number of digits of n-th prime written in base 4.
%H G. C. Greubel, <a href="/A163291/b163291.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = log_4 n + log_4 log n + O(1). - _Charles R Greathouse IV_, Mar 25 2010
%e 6th prime = 13 = 31_4, so a(6) = 2;
%e 7th prime = 17 = 101_4, so a(7) = 3;
%e 54th prime = 251 = 3323_4, so a(54) = 4;
%e 55th prime = 257 = 10001_4, so a(55) = 5.
%t IntegerLength[#, 4] & /@ Prime[Range[100]] (* _G. C. Greubel_, Dec 17 2016 *)
%o (PARI) a(n) = #digits(prime(n), 4); \\ _Michel Marcus_, Dec 18 2016
%Y Cf. A004678, A035100.
%K nonn,base
%O 1,3
%A _Juri-Stepan Gerasimov_, Jul 24 2009