On the equation $x^2_1 + x^2_2 + x^2_3 + x^2_4 = N$ with variables such that $x_1 x2_ x_3 x_4 + 1$ is an almost-prime
Todorova, T. L. ; Tolev, I D
Tatra Mountains Mathematical Publications, Tome 58 (2014), / Harvested from Mathematical Institute
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We consider Lagrange's equation$x^2_1 +x^2_2 +x^2_3 +x^2_4 = N$,where $ N$ is a sucientlylarge and odd integer, and prove that it has a solutionin natural numbers x1, \ldot,  x4such that $x_1 x_2 x_3 x_4 + 1$ has no more than 48 prime factors.

Publié le : 2014-01-01
DOI : https://doi.org/10.2478/tatra.v59i0.299 
@article{299,
     title = {On the equation $x^2\_1 + x^2\_2 + x^2\_3 + x^2\_4 = N$ with variables such that $x\_1 x2\_ x\_3 x\_4 + 1$ is an almost-prime},
     journal = {Tatra Mountains Mathematical Publications},
     volume = {58},
     year = {2014},
     doi = {10.2478/tatra.v59i0.299},
     language = {EN},
     url = {http://dml.mathdoc.fr/item/299}
}

Todorova, T. L.; Tolev, I D. On the equation $x^2_1 + x^2_2 + x^2_3 + x^2_4 = N$ with variables such that $x_1 x2_ x_3 x_4 + 1$ is an almost-prime. Tatra Mountains Mathematical Publications, Tome 58 (2014) . doi : 10.2478/tatra.v59i0.299. http://gdmltest.u-ga.fr/item/299/