1,2

a(n) = 0 if n is a perfect prime power or a prime such that n+2 is composite. The zero entries in other cases suggest a generalization of Fermat's last theorem.

a(n) = 2 if n and n+2 form a twin prime pair.

Table of n, a(n) for n=1..47.

a(12) = 63 as 12 + 63 = 75, 2^2*3 + 3^2*7 = 5^2*3, all have the prime signature p^2*q.

Sequence in context: A131728 A075115 A273528 * A260308 A079714 A286889

Adjacent sequences: A085077 A085078 A085079 * A085081 A085082 A085083

more,nonn

Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jul 01 2003

a(20)-a(47) from Max Alekseyev, Aug 12 2013

approved