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A050797 Numbers n such that n^2 - 1 is expressible as the sum of two nonzero squares in exactly one way. 5
3, 9, 17, 19, 33, 35, 73, 145, 161, 163, 195, 243, 393, 483, 513, 721, 723, 1153, 1763, 2177, 2305, 2593, 4803, 5185, 5833, 6273, 6963, 7057, 7395, 8713, 9523, 9603, 10083, 12483, 13923, 14113, 15875, 17425, 17673, 19043, 20737 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If the definition were changed from "nonzero squares" to "nonnegative squares", there would be just one additional term, 1. - T. D. Noe, May 27 2008

LINKS

T. D. Noe, Table of n, a(n) for n=1..300

Eric Weisstein, MathWorld: Sum of Squares Function

Index entries for sequences related to sums of squares

EXAMPLE

E.g. 393^2 - 1 = 28^2 + 392^2 only.

MATHEMATICA

twoSquaresQ[ n_] := (r = Reduce [0 < a <= b && n^2 - 1 == a^2 + b^2, {a, b}, Integers]; Head[r] === And); Select[ Range[21000], twoSquaresQ] (* Jean-Fran├žois Alcover, Oct 10 2011 *)

CROSSREFS

Cf. A050798, A050795.

Cf. A000161

Sequence in context: A174180 A106676 A050795 * A103967 A032400 A004621

Adjacent sequences:  A050794 A050795 A050796 * A050798 A050799 A050800

KEYWORD

nonn,nice

AUTHOR

Patrick De Geest, Sep 15 1999

EXTENSIONS

More terms from James A. Sellers

STATUS

approved

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Last modified July 19 12:26 EDT 2019. Contains 325159 sequences. (Running on oeis4.)