A025372 Numbers that are the sum of 4 nonzero squares in 7 or more ways.

130, 135, 138, 148, 150, 154, 162, 170, 172, 175, 178, 180, 182, 183, 186, 187, 189, 190, 195, 196, 198, 199, 202, 207, 210, 213, 214, 215, 217, 218, 220, 222, 223, 225, 226, 228, 229, 230, 231, 234, 235, 237, 238, 242, 243, 244, 245, 246, 247, 250, 252, 253, 255, 258

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Links

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

Crossrefs

Cf. A025335, A025363, A025371, A025373, A344800, A345150.

Programs

Maple

N:= 1000: # for terms <= N
B:= Vector(N):
for i from 1 while 4*i^2 <= N do
  for j from i while i^2 + 3*j^2 <= N do
    for k from j while i^2 + j^2 + 2*k^2 <= N do
      for l from k do
        m:= i^2 + j^2 + k^2 + l^2;
        if m > N then break fi;
        B[m]:= B[m]+1
od od od od:
select(t -> B[t] >= 7, [$1..N]); # Robert Israel, Oct 23 2020

Formula

{n: A025428(n) >= 7}. - R. J. Mathar, Jun 15 2018