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A020149 Pseudoprimes to base 21. 1
4, 10, 20, 55, 65, 85, 221, 703, 793, 1045, 1105, 1852, 2035, 2465, 3781, 4630, 5185, 5473, 5995, 6541, 7363, 8695, 8965, 9061, 10585, 10945, 11647, 13019, 13051, 13981, 14491, 17767, 18103, 18721, 19345, 19669, 19909, 21667, 22681, 23155, 24013, 25465 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Composite numbers n such that 21^(n-1) == 1 (mod n).

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

Index entries for sequences related to pseudoprimes

MATHEMATICA

base = 21; t = {}; n = 1; While[Length[t] < 100, n++; If[! PrimeQ[n] && PowerMod[base, n-1, n] == 1, AppendTo[t, n]]]; t (* T. D. Noe, Feb 21 2012 *)

CROSSREFS

Cf. A001567 (pseudoprimes to base 2).

Sequence in context: A189586 A019498 A237626 * A056412 A032275 A220828

Adjacent sequences:  A020146 A020147 A020148 * A020150 A020151 A020152

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified June 16 19:43 EDT 2019. Contains 324155 sequences. (Running on oeis4.)