A020672 Numbers of form x^2 + 9 y^2.

0, 1, 4, 9, 10, 13, 16, 18, 25, 34, 36, 37, 40, 45, 49, 52, 58, 61, 64, 72, 73, 81, 82, 85, 90, 97, 100, 106, 109, 117, 121, 130, 136, 144, 145, 148, 153, 157, 160, 162, 169, 178, 180, 181, 193, 196, 202, 205, 208, 225, 226, 229, 232, 234, 241, 244, 250, 256, 261, 265, 274

Offset: 1

Author

David W. Wilson

Keywords

• easy
• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..9600
• N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

Crossrefs

Primes: A068228.

Programs

Magma

[n: n in [0..300] | NormEquation(9, n) eq true]; // Vincenzo Librandi, Aug 31 2016

Mathematica

lim=300; k=9; Union@Flatten@Table[x^2 + k y^2, {y, 0, Sqrt[lim/k]}, {x, 0, Sqrt[lim-k y^2]}] (* Vincenzo Librandi, Aug 31 2016 *)