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A071522 Numbers n such that x^n + x^(n-1) + x^(n-2) + ... + x + 1 is irreducible over GF(5). 1
1, 2, 6, 16, 22, 36, 42, 46, 52, 72, 82, 96, 102, 106, 112, 136, 156, 166, 172, 192, 196, 222, 226, 232, 256, 262, 276, 282, 292, 306, 316, 346, 352, 372, 382, 396, 432, 442, 462, 466, 502, 522, 546, 556, 562, 576, 586, 592, 606, 612, 616, 646, 652, 672, 676 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers k = p - 1 such that p is a prime with primitive root 5. - Joerg Arndt, Jun 25 2020

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A019335(n) - 1. - Joerg Arndt, Jun 25 2020

MAPLE

filter:= proc(n)

isprime(n+1) and numtheory:-order(5, n+1)=n

end proc:

select(filter, [$1..1000]); # Robert Israel, Jun 25 2020

MATHEMATICA

Select[Prime[Range[1000]], MultiplicativeOrder[5, #] == # - 1&] - 1 (* Jean-François Alcover, Aug 16 2020 *)

PROG

(PARI) forprime(p=2, 10^3, if(p==5, next()); if(znorder(Mod(5, p))==p-1, print1(p-1, ", "))); \\ Joerg Arndt, Jun 25 2020

CROSSREFS

Cf. A071642. Contained in A006093.

Sequence in context: A085226 A260376 A330866 * A192532 A230853 A160620

Adjacent sequences: A071519 A071520 A071521 * A071523 A071524 A071525

KEYWORD

easy,nonn

AUTHOR

Robert G. Wilson v, Jun 22 2002

EXTENSIONS

a(1)=1 inserted by Robert Israel, Jun 24 2020

STATUS

approved

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Last modified February 3 21:17 EST 2023. Contains 360045 sequences. (Running on oeis4.)