A025294 Numbers that are the sum of 2 nonzero squares in 3 or more ways.

325, 425, 650, 725, 845, 850, 925, 1025, 1105, 1250, 1300, 1325, 1445, 1450, 1525, 1625, 1690, 1700, 1825, 1850, 1885, 2050, 2125, 2210, 2225, 2405, 2425, 2465, 2525, 2600, 2650, 2665, 2725, 2825, 2873, 2890, 2900, 2925, 3050, 3125, 3145, 3250, 3380

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Comments

A025426(a(n)) > 2. - Reinhard Zumkeller, Feb 26 2015

Links

• Robert Israel and Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 (first 2508 terms from Robert Israel)
• Index entries for sequences related to sums of squares

Crossrefs

Complement of A025285 relative to A007692. - Washington Bomfim, Oct 24 2010

Cf. A025426.

Programs

Haskell

a025294 n = a025294_list !! (n-1)
a025294_list = filter ((> 2) . a025426) [1..]
-- Reinhard Zumkeller, Feb 26 2015

Maple

  N:= 100000: # generate all entries <=N
SSQ:= {}: SSQ2:= {}: SSQ3:= {}:
for a from 1 to floor(sqrt(N)) do
  for b from a to floor(sqrt(N-a^2)) do
    n:= a^2 + b^2;
    if member(n,SSQ2) then SSQ3:= SSQ3 union {n}
    elif member(n,SSQ) then SSQ2:= SSQ2 union {n}
    else SSQ:= SSQ union {n}
    end if
end do end do:
SSQ3;  # Robert Israel, Jan 20 2013

Mathematica

okQ[n_] := Length[Select[PowersRepresentations[n, 2, 2][[All, 1]], Positive] ] > 2; Select[Range[5000], okQ] (* Jean-François Alcover, Mar 04 2019 *)