A281869 Number of sets of exactly nine positive integers <= n having a square element sum.

0, 1, 3, 14, 47, 121, 296, 660, 1358, 2646, 4905, 8704, 14887, 24649, 39651, 62175, 95286, 143038, 210732, 305210, 435195, 611697, 848494, 1162662, 1575195, 2111713, 2803273, 3687272, 4808464, 6220104, 7985229, 10178073, 12885638, 16209468, 20267579, 25196567

Offset

9,3

Links

Alois P. Heinz, Table of n, a(n) for n = 9..1000

Example

a(10) = 1: {1,2,3,4,5,7,8,9,10}.
a(11) = 3: {1,2,3,4,5,6,7,10,11}, {1,2,3,4,5,6,8,9,11}, {1,2,3,4,5,7,8,9,10}.

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, 8), j=isqrt(n-36)..isqrt(9*n-36)))
    end:
seq(a(n), n=9..60);

Crossrefs

Column k=9 of A281871.

Sequence in context: A027953 A264501 A104196 * A202144 A287426 A246149

Adjacent sequences: A281866 A281867 A281868 * A281870 A281871 A281872

Keyword

nonn

Author

Alois P. Heinz, Feb 01 2017

Status

approved