For even n > 4 = 2m, x^(2m) - y^(2m-2) = (x^m)^2 - y^((m-1))^2 is divisible by x^m - y^(m-1) which is not prime. This accounts for the omission of even powers in the definition.
Table of n, a(n) for n=1..11.
Sequence in context: A340823 A245442 A215239 * A240589 A180541 A103993
Adjacent sequences: A161746 A161747 A161748 * A161750 A161751 A161752
Cino Hilliard, Jun 17 2009
Incorrect program removed; definition confined to odd powers; added terms a(8)..a(11). - R. J. Mathar, Feb 27 2012