

A122785


Nonprimes m such that 8^m == 8 (mod m).


4



1, 4, 8, 9, 14, 21, 28, 45, 56, 63, 65, 105, 117, 133, 153, 231, 273, 292, 341, 481, 511, 561, 585, 645, 651, 861, 949, 1001, 1016, 1105, 1106, 1281, 1288, 1365, 1387, 1417, 1541, 1649, 1661, 1729, 1736, 1785, 1905, 2044, 2047, 2169, 2465, 2501, 2696, 2701, 2821, 3145, 3171, 3201, 3277, 3605, 3641, 4005
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OFFSET

1,2


COMMENTS

Theorem: If both numbers q and 2q1 are primes and m=q*(2q1) then 8^m==8 (mod m) (m is in the sequence) iff q is of the form 4k+1. 2701,18721,49141,104653,226801,665281,721801,... are such terms.


LINKS

Table of n, a(n) for n=1..58.


MAPLE

q:= m> not isprime(m) and 8&^m mod m = 8 mod m:
select(q, [$1..5000])[]; # Alois P. Heinz, Apr 19 2022


MATHEMATICA

Select[Range[6000], ! PrimeQ[ # ] && Mod[8^#, # ] == Mod[8, # ] &]


CROSSREFS

Cf. A020137, A001567.
Sequence in context: A085711 A182491 A281686 * A280450 A137055 A078177
Adjacent sequences: A122782 A122783 A122784 * A122786 A122787 A122788


KEYWORD

nonn


AUTHOR

Farideh Firoozbakht, Sep 12 2006


EXTENSIONS

Missing a(8)a(18) inserted by Georg Fischer, Apr 19 2022


STATUS

approved



