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A034021 Numbers that are primitively but not imprimitively represented by x^2+xy+y^2. 0
0, 1, 3, 7, 13, 19, 21, 31, 37, 39, 43, 57, 61, 67, 73, 79, 91, 93, 97, 103, 109, 111, 127, 129, 133, 139, 151, 157, 163, 181, 183, 193, 199, 201, 211, 217, 219, 223, 229, 237, 241, 247, 259, 271, 273, 277, 283, 291, 301, 307, 309, 313, 327, 331, 337, 349, 367 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also numbers that are squarefree and primitively represented by x^2+x*y+y^2. - Frank M Jackson, Nov 08 2013

LINKS

Table of n, a(n) for n=1..57.

MATHEMATICA

lst = {}; Do[k=x^2+x*y+y^2; If[(SquareFreeQ[k] && GCD[x, y]==1) || k==0, AppendTo[lst, k]], {x, 0, 100}, {y, 0, x}]; Union@lst (* Frank M Jackson, Nov 08 2013 *)

CROSSREFS

Cf. A034017, A003136, A045897.

Sequence in context: A214696 A118667 A034017 * A216516 A038978 A133387

Adjacent sequences:  A034018 A034019 A034020 * A034022 A034023 A034024

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Extended by Ray Chandler, Jan 29 2009

STATUS

approved

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Last modified December 20 15:53 EST 2014. Contains 252266 sequences.