OFFSET
1,2
COMMENTS
a(n)^2 are the perfect squares in A128399.
a(10) > 10^13. [From Max Alekseyev]
MATHEMATICA
Do[g=PowerMod[19, n^2, n^4]-1; If[IntegerQ[g/n^4], Print[n]], {n, 1, 10000}]
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Mar 28 2007
EXTENSIONS
a(9) from D. S. McNeil, Mar 02 2009
STATUS
approved