A211455 - OEIS

A211455

The number of bases b for which A181780(n) is a Fermat pseudoprime.

2, 2, 2, 2, 2, 2, 2, 6, 4, 2, 2, 2, 2, 2, 14, 4, 2, 2, 2, 2, 2, 14, 2, 34, 2, 2, 2, 14, 2, 2, 2, 6, 2, 8, 2, 2, 2, 2, 2, 34, 2, 2, 2, 14, 2, 2, 14, 2, 2, 2, 2, 14, 10, 2, 2, 10, 4, 2, 2, 14, 4, 2, 2, 8, 6, 2, 2, 2, 14, 2, 2, 2, 2, 2, 34, 2, 14, 6, 38, 6, 2, 2

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OFFSET

1,1

COMMENTS

Sequences A211456 and A211457 give the smallest and largest bases b; A211458 lists all bases.

Every term in this sequence is even. - Geoffrey Critzer, Apr 08 2015

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

Index entries for sequences related to pseudoprimes

FORMULA

a(n) = A063994(m) - 2 for odd m in A181780. a(n) = A063994(m) - 1 for even m in A181780. - Thomas Ordowski, Dec 13 2013

MATHEMATICA

t = {}; n = 1; While[Length[t] < 100, n++; If[! PrimeQ[n], s = Select[Range[2, n-2], PowerMod[#, n-1, n] == 1 &]; If[s != {}, AppendTo[t, {n, Length[s], s}]]]]; Transpose[t][[2]]

f[n_] := If[ PrimeQ@ n, {}, Count[ Table[ PowerMod[k, n - 1, n], {k, 2, n - 2}], 1]] /. {0 -> {}}; Array[f, 237] // Flatten (* Robert G. Wilson v, Apr 08 2015 *)

CROSSREFS

Cf. A181780, A211456, A211457, A211458.

Sequence in context: A244462 A063790 A334510 * A214079 A202742 A248771

Adjacent sequences: A211452 A211453 A211454 * A211456 A211457 A211458

KEYWORD

nonn

AUTHOR

T. D. Noe, Apr 13 2012

STATUS

approved