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

7,3

Links

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

Example

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}.

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

Crossrefs

Column k=7 of A281871.

Sequence in context: A248731 A279101 A276599 * A298806 A362179 A033539

Adjacent sequences: A281864 A281865 A281866 * A281868 A281869 A281870

Keyword

nonn

Author

Alois P. Heinz, Feb 01 2017

Status

approved