login
Number of primes less than 10^n having at least one digit 4.
7

%I #14 Jul 21 2015 06:07:34

%S 0,3,32,326,3231,31953,310456,3000349,28922364,278508004,2680391313,

%T 25793058269,248228108241,2389543008906

%N Number of primes less than 10^n having at least one digit 4.

%e a(2) = 3 because of the 25 primes less than 10^2, 3 have at least one digit 4.

%t NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; c = 0; p = 1; Do[ While[ p = NextPrim[p]; p < 10^n, If[ Position[ IntegerDigits[p], 4] != {}, c++ ]]; Print[c]; p--, {n, 1, 8}] (* _Robert G. Wilson v_, Feb 02 2004 *)

%Y a(n) + A091638(n) = A006880(n).

%Y Cf. A091644, A091645, A091646, A091647, A091706, A091707, A091708, A091709, A091710.

%K nonn,base

%O 1,2

%A _Enoch Haga_, Jan 30 2004

%E Edited and extended by _Robert G. Wilson v_, Feb 02 2004

%E 3 more terms from _Ryan Propper_, Aug 21 2005

%E a(13) from _Robert Price_, Nov 11 2013

%E a(14) from _Giovanni Resta_, Jul 21 2015