A020676 Numbers of form 2 x^2 + 9 y^2.

0, 2, 8, 9, 11, 17, 18, 27, 32, 36, 38, 41, 44, 50, 54, 59, 68, 72, 81, 83, 86, 89, 98, 99, 107, 108, 113, 128, 131, 134, 137, 144, 146, 152, 153, 162, 164, 171, 176, 179, 194, 198, 200, 209, 216, 225, 227, 233, 236, 242, 243, 251, 257, 272, 275, 278, 281, 288, 297, 306, 323

Offset: 1

Author

David W. Wilson

Keywords

• easy
• nonn

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000
• N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

Crossrefs

Subsequences include A001105, A016766.

Cf. A106949 (prime terms).

Programs

Mathematica

With[{upto = 350}, Select[Union[2#[[1]]^2 + 9#[[2]]^2&/@Tuples[Range[0, Ceiling[Sqrt[upto^2/2]]], 2]], # <= upto &]] (* Harvey P. Dale, May 30 2017 *)