A086122 - OEIS

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A086122

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

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

(list; graph; refs; listen; history; text; internal format)

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

A003464 INTERSECT A000040.

MATHEMATICA

Do[f=(5^n-1)/4; If[PrimeQ[f], Print[{n, f}]], {n, 1, 1000}] (* Alexander Adamchuk, Jan 23 2007 *)