OFFSET
1,2
COMMENTS
Numbers n such that p=10n+1 is prime and the greatest prime divisor of p-1 is 5.
MATHEMATICA
Do[If[Take[FactorInteger[EulerPhi[10n+1]][[ -1]], 1]=={5} && PrimeQ[10n+1], Print[n]], {n, 1, 10000}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski, Dec 13 2006
EXTENSIONS
Edited by Don Reble, Apr 24 2007
STATUS
approved