OFFSET
1,1
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
6 is in the sequence since gcd(6, 21) = 3 and 6 does not divide 21^e with integer e >= 0.
5 is not in the sequence since it is coprime to 21.
3 is not in the sequence since 3 | 21.
9 is not in the sequence since 9 | 21^2.
MAPLE
filter:= proc(n) local g;
g:= igcd(n, 21);
if g = 1 or g = n then return false fi;
3^padic:-ordp(n, 3)*7^padic:-ordp(n, 7) < n
end proc:
select(filter, [$1..200]); # Robert Israel, Aug 28 2019
MATHEMATICA
With[{nn = 161, k = 21}, Select[Range@ nn, And[1 < GCD[#, k] < #, PowerMod[k, Floor@ Log2@ nn, #] != 0] &]]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Michael De Vlieger, Aug 22 2019
STATUS
approved