Primes of the form 3*x^2+x*y-3*y^2 (as well as of the form 3*x^2+7*x*y+y^2).
3, 7, 11, 37, 41, 47, 53, 67, 71, 73, 83, 101, 107, 127, 137, 139, 149, 151, 157, 173
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Sat Oct 10 20:36:40 CEST 2009 [seqfan] Re: A006451 = n such that n*(n+1)/2+1 is square?