A085625 Numbers that are the sum of 2 squares in exactly 2 ways.

25, 50, 65, 85, 100, 125, 130, 145, 169, 170, 185, 200, 205, 221, 225, 250, 260, 265, 289, 290, 305, 338, 340, 365, 370, 377, 400, 410, 442, 445, 450, 481, 485, 493, 500, 505, 520, 530, 533, 545, 565, 578, 580, 585, 610, 629, 676, 680, 685, 689, 697, 730

Offset

1,1

Comments

Wells erroneously writes that this sequence begins as 50, 65, 85, 145, ... . - Stefano Spezia, Sep 07 2024

References

David Wells, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, Revised edition 1987. See p. 125.

Links

Robert Price, Table of n, a(n) for n = 1..16794

Formula

n such that A000161(n) = 2.

Example

a(3) = 65 because 65 = 8^2 + 1^2 = 7^2 + 4^2;
a(4) = 85 because 85 = 9^2 + 2^2 = 7^2 + 6^2.

Mathematica

Select[Range[730], Length[PowersRepresentations[#, 2, 2]]==2 &] (* Stefano Spezia, Sep 07 2024 *)

Crossrefs

Cf. A000161, A000446, A224443, A294282, A295153, A295489, A295748.

Sequence in context: A354379 A009177 A118882 * A116490 A230213 A338890

Adjacent sequences: A085622 A085623 A085624 * A085626 A085627 A085628

Keyword

nonn,changed

Author

Hugo Pfoertner, Jul 09 2003

Status

approved