OFFSET
1,1
LINKS
MATHEMATICA
Select[FromDigits /@ NestList["2" <> # &, "7", 10^3], PrimeQ] (* Mikk Heidemaa, Nov 18 2015 *)
PROG
(PARI) list(lim)=for(i=0, lim, m=20*(10^i-1)/9 + 7; if(isprime(m), print1(m, " , "))) \\ Anders Hellström, Nov 18 2015
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Rick L. Shepherd, Mar 26 2004
STATUS
approved