OFFSET
1,1
COMMENTS
Complement to composite numbers: 4, 8, 9, 10, 14, 16, 18, 21, 25, 27, 32, 33, 35, 36, 39, 42, 44, 45, 49, 50, 51, 52, 54, 55, 57, ... - R. J. Mathar, May 16 2008
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
22 is a term since 4^22 mod 22 = 16.
MAPLE
filter:= proc(n) local k, j;
if isprime(n) then return false fi;
k:= 4 &^ n mod n;
j:= padic:-ordp(k, 2);
k>1 and j::even and k = 2^j
end proc:
select(filter, [$4..1000]); # Robert Israel, Dec 03 2019
MATHEMATICA
Select[ Range@ 161, IntegerQ@ Log[4, PowerMod[4, #, # ]] &]
PROG
(Magma) [k:k in [2..200]| not IsPrime(k) and not IsZero(a) and (PrimeDivisors(a) eq [2]) and &+[j[1]*j[2]: j in Factorization(a) ] mod 4 eq 0 where a is 4^k mod k]; // Marius A. Burtea, Dec 04 2019
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Robert G. Wilson v, Apr 17 2007
EXTENSIONS
Corrected and extended by R. J. Mathar, May 16 2008
STATUS
approved