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A281867 Number of sets of exactly seven positive integers <= n having a square element sum. 2
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 (list; graph; refs; listen; history; text; internal format)
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 A033539 A020748

Adjacent sequences:  A281864 A281865 A281866 * A281868 A281869 A281870

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Feb 01 2017

STATUS

approved

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Last modified February 15 22:28 EST 2019. Contains 320138 sequences. (Running on oeis4.)