OFFSET
1,1
COMMENTS
Complement to composite numbers: 4, 8, 16, 18, 25, 27, 32, 35, 36, 42, 45, 49, 50, 54, 55, 64, 70, 75, 77, 81, 88, 91, 95, 98, 99, ....
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
15 is a term since 2^15 mod 15 = 8.
MAPLE
filter:= proc(n) local k;
if isprime(n) then return false fi;
k:= 2 &^ n mod n;
k > 1 and k = 2^padic:-ordp(k, 2)
end proc:
select(filter, [$4..1000]); # Robert Israel, Dec 03 2019
MATHEMATICA
Select[Range@ 141, IntegerQ@ Log[2, PowerMod[2, #, # ]] &]
PROG
(Magma) [k:k in [2..150]| not IsPrime(k) and not IsZero(a) and (PrimeDivisors(a) eq [2]) where a is 2^k mod k ]; // Marius A. Burtea, Dec 04 2019
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Robert G. Wilson v, Apr 17 2007
STATUS
approved