OFFSET
1
COMMENTS
Characteristic function for A206075, apart from its initial term.
LINKS
EXAMPLE
For n = 25 we know that it is composite as 25 = 5*5, but nevertheless, its binary representation "11001" encodes a (0,1)-polynomial x^4 + x^3 + 1, which is irreducible when factored over Q, thus a(25) = 1.
PROG
(PARI) A305821(n) = (!isprime(n) && polisirreducible(Pol(binary(n))));
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jun 10 2018
STATUS
approved