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A227180 Composite numbers n such that b^(n-1) == 1 (mod n) implies b == -1 or +1 (mod n). 2
4, 6, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 27, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 54, 56, 58, 60, 62, 64, 68, 72, 74, 78, 80, 81, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 114, 116, 118, 120, 122, 126, 128, 132, 134, 136, 138, 140, 142, 144, 146, 150, 152, 156, 158, 160, 162, 164, 166, 168, 170 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The sequence is the union of A111305 with {3^k | k > 1}.

The composite numbers not in this sequence are the Fermat pseudoprimes A181780.

LINKS

Table of n, a(n) for n=1..77.

MATHEMATICA

FQ[k_]:= Block[{}, GCD[EulerPhi[k], k-1]==1||IntegerQ[Log[3, k]]]; Select[Range[4, 170], FQ]

PROG

(PARI) is(n)=for(b=2, n-2, if(Mod(b, n)^(n-1)==1, return(0))); !isprime(n) \\ Charles R Greathouse IV, Dec 22 2016

CROSSREFS

Cf. A111305, A181780, A209211.

Sequence in context: A327776 A102554 A070810 * A129930 A128510 A109289

Adjacent sequences:  A227177 A227178 A227179 * A227181 A227182 A227183

KEYWORD

nonn

AUTHOR

Emmanuel Vantieghem, Jul 03 2013

STATUS

approved

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Last modified December 4 12:33 EST 2020. Contains 338923 sequences. (Running on oeis4.)