A086122 Primes of the form (5^k-1)/4.

31, 19531, 12207031, 305175781, 177635683940025046467781066894531, 14693679385278593849609206715278070972733319459651094018859396328480215743184089660644531, 35032461608120426773093239582247903282006548546912894293926707097244777067146515037165954709053039550781

Offset: 1

Author

Labos Elemer, Jul 23 2003

Keywords

• nonn

Comments

Corresponding exponents k are listed in A004061. - Alexander Adamchuk, Jan 23 2007

Crossrefs

Cf. A000668, A076481.

Cf. A003463, A004061, A074479.

Programs

Mathematica

Do[f=(5^n-1)/4;If[PrimeQ[f],Print[{n,f}]],{n,1,1000}] (* Alexander Adamchuk, Jan 23 2007 *)
Select[(5^Range[300]-1)/4,PrimeQ] (* Harvey P. Dale, Dec 11 2016 *)

Formula

a(n) = (5^A004061(n) - 1)/4 = A003463[ A004061(n) ]. - Alexander Adamchuk, Jan 23 2007

A003464 INTERSECT A000040.

Extensions

More terms from Alexander Adamchuk, Jan 23 2007