A281867 Number of sets of exactly seven positive integers <= n having a square element sum.

0, 0, 4, 10, 25, 60, 124, 238, 435, 750, 1237, 1973, 3047, 4574, 6706, 9624, 13546, 18742, 25533, 34292, 45469, 59585, 77238, 99127, 126048, 158897, 198713, 246663, 304057, 372374, 453245, 548479, 660104, 790372, 941770, 1117035, 1319141, 1551314, 1817124

Offset: 7

Author

Alois P. Heinz, Feb 01 2017

Keywords

• nonn

Examples

			a(9) = 4: {1,2,3,6,7,8,9}, {1,2,4,5,7,8,9}, {1,3,4,5,6,8,9}, {2,3,4,5,6,7,9}.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 7..1000

Crossrefs

Column k=7 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, 6), j=isqrt(n-21)..isqrt(7*n-21)))
    end:
seq(a(n), n=7..60);