A049241 - OEIS

A049241

Smallest nonnegative value taken on by 2*x^2 - n*y^2 for an infinite number of integer pairs (x, y).

1, 0, 2, 2, 2, 2, 1, 0, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 1, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 2, 1, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 2, 2, 2, 2, 1, 2, 2

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OFFSET

1,3

LINKS

Table of n, a(n) for n=1..105.

MATHEMATICA

f[n_, z_] := FindInstance[x > 0 && y > 0 && 2*x^2 - n*y^2 == z, {x, y}, Integers, 1]; a[n_] := For[z = 0, True, z = z + GCD[n, 2], fz = f[n, z]; If[fz =!= {}, Print["a(", n, ") = ", z, " {x, y} = ", {x, y} /. fz[[1]]]; Return[z]]]; a[81] := (Print["a(81) = ", 2, " {x, y} = ", {19601, 3080}]; 2); Table[TimeConstrained[a[n], 300], {n, 1, 105}] (* Jean-François Alcover, Oct 09 2016 *)

CROSSREFS

Sequence in context: A318722 A174344 A340171 * A321858 A334235 A230415

Adjacent sequences: A049238 A049239 A049240 * A049242 A049243 A049244

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved