A281868 Number of sets of exactly eight positive integers <= n having a square element sum.

1, 1, 3, 13, 34, 86, 197, 405, 786, 1446, 2532, 4263, 6938, 10953, 16837, 25281, 37165, 53605, 75999, 106075, 145951, 198199, 265921, 352825, 463320, 602609, 776797, 993007, 1259503, 1585839, 1983013, 2463629, 3042066, 3734648, 4559849, 5538527, 6694180

Offset

8,3

Links

Alois P. Heinz, Table of n, a(n) for n = 8..1000

Example

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

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, 7), j=isqrt(n-28)..isqrt(8*n-28)))
    end:
seq(a(n), n=8..60);

Crossrefs

Column k=8 of A281871.

Sequence in context: A211801 A016061 A154154 * A137976 A095661 A058214

Adjacent sequences: A281865 A281866 A281867 * A281869 A281870 A281871

Keyword

nonn

Author

Alois P. Heinz, Feb 01 2017

Status

approved