login
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.
3
23357, 23557, 2235557, 2335577, 2355557, 22222222357, 22222333577, 22223333357, 22223335577, 22223335777, 22223357777, 22233577777, 22333355777, 22335555577, 22355555557, 22355555777, 23333335577
OFFSET
1,1
LINKS
MAPLE
F:= proc(d) local Res, x2, x3, x5, x7, x;
Res:= NULL:
for x2 from d-3 to 1 by -1 do
for x3 from d-x2-2 to 1 by -1 do
for x5 from d-x2-x3-1 to 1 by -1 do
x7:= d-x2-x3-x5;
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));
if isprime(x) then Res:= Res, x fi
od od od:
Res;
end proc:
seq(F(ithprime(i)), i=3..6); # Robert Israel, Feb 03 2019
CROSSREFS
Cf. A153770.
Sequence in context: A251111 A205834 A184229 * A252944 A246891 A189656
KEYWORD
nonn,base
AUTHOR
Lekraj Beedassy, Jan 01 2009
EXTENSIONS
Extended by Ray Chandler, Jan 07 2009
STATUS
approved