A020689 Numbers of form 6 x^2 + 7 y^2.

0, 6, 7, 13, 24, 28, 31, 34, 52, 54, 61, 63, 69, 82, 87, 96, 103, 112, 117, 118, 124, 136, 150, 157, 159, 166, 175, 178, 181, 199, 208, 213, 216, 223, 229, 244, 252, 258, 262, 271, 276, 279, 294, 301, 306, 322, 325, 328, 343, 348, 349, 357, 367, 384, 391, 397, 402, 406

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..21685

N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

Prog

(PARI) isA020689(n) = { my(r); forstep(y=sqrtint(ceil(n/7)), 0, -1, r = (n-7*(y^2)); if(!(r%6) && issquare(r/6), return(1))); (0); }; \\ Antti Karttunen, Jan 04 2025

Crossrefs

Cf. A054182.

Sequence in context: A041749 A042723 A160825 * A128844 A128850 A042025

Adjacent sequences: A020686 A020687 A020688 * A020690 A020691 A020692

Keyword

easy,nonn,changed

Author

David W. Wilson

Status

approved