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

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

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..7.

Formula

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

Equals A003463 INTERSECT A000040.

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 *)

Prog

(PARI) forprime(p=2, 1e3, my(n=5^p\4); if(ispseudoprime(n), print1(n", "))) \\ Sjoerd J. Schaper, Nov 23 2025

Crossrefs

Cf. A000668, A076481.

Cf. A003463, A004061, A074479.

Sequence in context: A161395 A215610 A292009 * A239167 A263585 A176349

Adjacent sequences: A086119 A086120 A086121 * A086123 A086124 A086125

Keyword

nonn

Author

Labos Elemer, Jul 23 2003

Extensions

More terms from Alexander Adamchuk, Jan 23 2007

Status

approved