OFFSET
1,1
COMMENTS
MATHEMATICA
Select[Range[250000], FactorInteger[#^2-1][[-1, 1]]==13&]
PROG
(Magma) [ n: n in [2..250000] | m eq 13 where m is D[#D] where D is PrimeDivisors(n^2-1) ]; // Klaus Brockhaus, Feb 18 2011
(PARI) is(n)=n=n^2-1; forprime(p=2, 11, n/=p^valuation(n, p)); n>1 && 13^valuation(n, 13)==n \\ Charles R Greathouse IV, Jul 01 2013
CROSSREFS
KEYWORD
fini,nonn,full
AUTHOR
Artur Jasinski, Oct 21 2010
STATUS
approved