A281866 Number of sets of exactly six positive integers <= n having a square element sum.

0, 1, 3, 7, 19, 39, 74, 134, 227, 365, 568, 854, 1247, 1777, 2479, 3392, 4562, 6043, 7898, 10194, 13010, 16428, 20547, 25474, 31330, 38248, 46370, 55846, 66843, 79544, 94161, 110917, 130044, 151782, 176391, 204159, 235410, 270487, 309744, 353539, 402255

Offset

6,3

Links

Alois P. Heinz, Table of n, a(n) for n = 6..1000

Example

a(7) = 1: {1,2,4,5,6,7}.
a(8) = 3: {1,2,3,4,7,8}, {1,2,3,5,6,8}, {1,2,4,5,6,7}.

Maple

b:= proc(n, i, t) option remember;
      `if`(i<t, 0, `if`(n=0, `if`(t=0, 1, 0),
      `if`(t<1 or n<t*(t+1)/2 or n>(t+1)*(2*i-t)/2, 0,
      `if`(i>n, 0, b(n-i, i-1, t-1))+b(n, i-1, t))))
    end:
a:= proc(n) option remember; `if`(n<0, 0, a(n-1)+add(
       b(j^2-n, n-1, 5), j=isqrt(n-15)..isqrt(6*n-15)))
    end:
seq(a(n), n=6..60);

Crossrefs

Column k=6 of A281871.

Sequence in context: A047025 A222465 A239416 * A173114 A163572 A292775

Adjacent sequences: A281863 A281864 A281865 * A281867 A281868 A281869

Keyword

nonn

Author

Alois P. Heinz, Feb 01 2017

Status

approved