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

Author

Alois P. Heinz, Feb 01 2017

Keywords

• nonn

Examples

			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}.
		

Links

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

Crossrefs

Column k=6 of A281871.

Programs

Maple

b:= proc(n, i, t) option remember;
      `if`(i(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);