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A090088 Smallest even pseudoprimes to odd base=2n-1, not necessarily exceeding n. See also A007535 and A090086, A090087. 4
4, 286, 4, 6, 4, 10, 4, 14, 4, 6, 4, 22, 4, 26, 4, 6, 4, 34, 4, 38, 4, 6, 4, 46, 4, 10, 4, 6, 4, 58, 4, 62, 4, 6, 4, 10, 4, 74, 4, 6, 4, 82, 4, 86, 4, 6, 4, 94, 4, 14, 4, 6, 4, 106, 4, 10, 4, 6, 4, 118, 4, 122, 4, 6, 4, 10, 4, 134, 4, 6, 4, 142, 4, 146, 4, 6, 4, 14, 4, 158, 4, 6, 4, 166, 4, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For an even base there are no even pseudoprimes.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16520

Antti Karttunen, Data supplement: n, a(n) computed for n =  1..100000

FORMULA

a(n) = Min_{x=even number; (-1 + n^(x-1)) mod x = 0}.

EXAMPLE

n=2, 2n-2=3 as base, smallest relevant power is -1+2^(286-1) which is divisible by 286.

MATHEMATICA

Array[Block[{k = 4}, While[PowerMod[2 # - 1, k - 1, k] != 1, k += 2]; k] &, 86] (* Michael De Vlieger, Nov 13 2018 *)

PROG

(PARI) A090088(n) = { forstep(k=4, oo, 2, if(1==(Mod(n+n-1, k)^(k-1)), return (k)); ); } \\ (After code in A090086) - Antti Karttunen, Nov 10 2018

CROSSREFS

Cf. A007535, A090986, A090987, A090089.

Sequence in context: A074309 A113256 A259495 * A253233 A242997 A221135

Adjacent sequences:  A090085 A090086 A090087 * A090089 A090090 A090091

KEYWORD

nonn

AUTHOR

Labos Elemer, Nov 25 2003

STATUS

approved

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Last modified August 19 07:13 EDT 2022. Contains 356216 sequences. (Running on oeis4.)