OFFSET
1,1
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
filter:= k -> not isprime(k) and 2 &^ (k*(k-1)) mod (k^2) = 1:
select(filter, [$4..10000]); # Robert Israel, Feb 07 2019
MATHEMATICA
Select[Range[3300], And[CompositeQ@ #, PowerMod[2, # (# - 1), #^2] == 1] &] (* Michael De Vlieger, Feb 03 2019 *)
PROG
(PARI) isok(k) = !isprime(k) && ((2^(k*(k-1)) % k^2) == 1); \\ Michel Marcus, Feb 01 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski, Feb 01 2019
STATUS
approved