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A086122 Primes of the form (5^k-1)/4. 7
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 *)

Select[(5^Range[300]-1)/4, PrimeQ] (* Harvey P. Dale, Dec 11 2016 *)

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

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Last modified December 13 03:41 EST 2019. Contains 329968 sequences. (Running on oeis4.)