A127315 Numbers n such that n^4 divides 19^(n^2)-1.

1, 2, 3, 6, 42, 78, 546, 1806, 23478

Offset: 1

Author

Alexander Adamchuk, Mar 28 2007

Keywords

• hard
• more
• nonn

Comments

a(n)^2 are the perfect squares in A128399.

a(10) > 10^13. [From Max Alekseyev]

Crossrefs

Cf. A128399 = numbers n such that n^2 divides 19^n-1.

Programs

Mathematica

Do[g=PowerMod[19,n^2,n^4]-1;If[IntegerQ[g/n^4],Print[n]],{n,1,10000}]

Extensions

a(9) from D. S. McNeil, Mar 02 2009