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 A281867 Number of sets of exactly seven positive integers <= n having a square element sum. 2

%I

%S 0,0,4,10,25,60,124,238,435,750,1237,1973,3047,4574,6706,9624,13546,

%T 18742,25533,34292,45469,59585,77238,99127,126048,158897,198713,

%U 246663,304057,372374,453245,548479,660104,790372,941770,1117035,1319141,1551314,1817124

%N Number of sets of exactly seven positive integers <= n having a square element sum.

%H Alois P. Heinz, <a href="/A281867/b281867.txt">Table of n, a(n) for n = 7..1000</a>

%e 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}.

%p b:= proc(n, i, t) option remember;

%p `if`(i<t, 0, `if`(n=0, `if`(t=0, 1, 0),

%p `if`(t<1 or n<t*(t+1)/2 or n>(t+1)*(2*i-t)/2, 0,

%p `if`(i>n, 0, b(n-i, i-1, t-1))+b(n, i-1, t))))

%p end:

%p a:= proc(n) option remember; `if`(n<0, 0, a(n-1)+add(

%p b(j^2-n, n-1, 6), j=isqrt(n-21)..isqrt(7*n-21)))

%p end:

%p seq(a(n), n=7..60);

%Y Column k=7 of A281871.

%K nonn

%O 7,3

%A _Alois P. Heinz_, Feb 01 2017

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Last modified August 4 19:17 EDT 2020. Contains 336202 sequences. (Running on oeis4.)