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A281865 Number of sets of exactly five positive integers <= n having a square element sum. 2
0, 1, 2, 6, 13, 24, 43, 71, 110, 166, 242, 341, 469, 633, 838, 1091, 1400, 1774, 2219, 2745, 3364, 4089, 4933, 5904, 7015, 8279, 9713, 11338, 13172, 15230, 17524, 20071, 22895, 26025, 29485, 33294, 37472, 42040, 47026, 52463, 58383, 64816, 71785, 79318, 87444 (list; graph; refs; listen; history; text; internal format)
OFFSET

5,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 5..1000

EXAMPLE

a(6) = 1: {1,2,3,4,6}.

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

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

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, 4), j=isqrt(n-10)..isqrt(5*n-10)))

    end:

seq(a(n), n=5..60);

CROSSREFS

Column k=5 of A281871.

Sequence in context: A003600 A283551 A000135 * A267698 A065220 A048094

Adjacent sequences:  A281862 A281863 A281864 * A281866 A281867 A281868

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Feb 01 2017

STATUS

approved

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Last modified February 19 10:54 EST 2019. Contains 320310 sequences. (Running on oeis4.)