cp's OEIS Frontend

A153771 Primes with a prime number of digits and using all of the prime digits 2, 3, 5, 7 repeated in strings, in that order.

%I A153771 #9 Feb 04 2019 02:59:54
%S A153771 23357,23557,2235557,2335577,2355557,22222222357,22222333577,
%T A153771 22223333357,22223335577,22223335777,22223357777,22233577777,
%U A153771 22333355777,22335555577,22355555557,22355555777,23333335577
%N A153771 Primes with a prime number of digits and using all of the prime digits 2, 3, 5, 7 repeated in strings, in that order.
%H A153771 Robert Israel, <a href="/A153771/b153771.txt">Table of n, a(n) for n = 1..10000</a>
%p A153771 F:= proc(d) local Res, x2, x3, x5, x7,x;
%p A153771   Res:= NULL:
%p A153771   for x2 from d-3 to 1 by -1 do
%p A153771     for x3 from d-x2-2 to 1 by -1 do
%p A153771       for x5 from d-x2-x3-1 to 1 by -1 do
%p A153771         x7:= d-x2-x3-x5;
%p A153771         x:= 7/9*(10^x7-1) + 5/9*(10^(x5+x7)-10^x7) + 3/9*(10^(x3+x5+x7)-10^(x5+x7)) + 2/9*(10^d-10^(x3+x5+x7));
%p A153771         if isprime(x) then Res:= Res, x fi
%p A153771   od od od:
%p A153771   Res;
%p A153771 end proc:
%p A153771 seq(F(ithprime(i)),i=3..6); # _Robert Israel_, Feb 03 2019
%Y A153771 Cf. A153770.
%K A153771 nonn,base
%O A153771 1,1
%A A153771 _Lekraj Beedassy_, Jan 01 2009
%E A153771 Extended by _Ray Chandler_, Jan 07 2009