Geodesic
The numbers $a^2 + b^2 - dc^2$
Journal of integer sequences, Tome 18 (2015) no. 2.

Voir la notice de l'article provenant de la source Electronic Library of Mathematics

Summary: We say that a positive integer $d$ is special if for every integer $m$ there exist nonzero integers $a, b, c$ such that $m = a^{2} + b^{2} - dc^{2}$. In this note we present examples and some properties of special numbers. Moreover, we present an infinite sequence of special numbers.
Classification : 11D09, 11B99
Keywords: pell's equation, sum of squares 
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     author = {Nowicki, Andrzej},
     title = {The numbers $a^2 + b^2 - dc^2$},
     journal = {Journal of integer sequences},
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     number = {2},
     year = {2015},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2015__18_2_a0/}
}
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Nowicki, Andrzej. The numbers $a^2 + b^2 - dc^2$. Journal of integer sequences, Tome 18 (2015) no. 2. http://geodesic.mathdoc.fr/item/JIS_2015__18_2_a0/