A000443 Numbers that are the sum of 2 squares in exactly 3 ways.

325, 425, 625, 650, 725, 845, 850, 925, 1025, 1250, 1300, 1325, 1445, 1450, 1525, 1690, 1700, 1825, 1850, 2050, 2225, 2425, 2500, 2525, 2600, 2650, 2725, 2825, 2873, 2890, 2900, 2925, 3050, 3125, 3380, 3400, 3425, 3650, 3700, 3725, 3757, 3825, 3925, 4100

Offset: 1

Author

N. J. A. Sloane and J. C. Lagarias (lagarias(AT)umich.edu)

Keywords

• nonn

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to sums of squares

Programs

Mathematica

nn = 70; lim = nn^2; t = Table[0, {lim}]; Do[k = x^2 + y^2; If[0 < k <= lim, t[[k]]++], {x, 0, nn}, {y, x, nn}]; Flatten[Position[t, 3]] (* T. D. Noe, Jun 20 2012 *)
Select[Range[4500],Length[PowersRepresentations[#,2,2]]==3&] (* Harvey P. Dale, Jun 02 2017 *)