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%I #12 Oct 23 2015 17:01:51
%S 0,1,4,7,4,7,10,13,16,9,12,15,18,21,24,27,16,19,22,25,28,31,34,37,40,
%T 25,28,31,34,37,40,43,46,49,52,55,36,39,42,45,48,51,54,57,60,63,66,69,
%U 72,49,52,55,58,61,64,67,70,73,76,79,82,85,88,91,64,67,70,73,76,79,82,85,88,91
%N a(n) = n + 2 * square excess of n.
%H Robert Israel, <a href="/A094765/b094765.txt">Table of n, a(n) for n = 0..10000</a>
%H S. H. Weintraub, <a href="http://www.jstor.org/stable/4145074">An interesting recursion</a>, Amer. Math. Monthly, 111 (No. 6, 2004), 528-530.
%F a(n) = n + 2*A053186(n).
%F G.f.: 3*x/(1-x)^2 - (2/(1-x)) * Sum_{k>=1} (2*k-1)*x^(k^2). The sum is related to Jacobi theta functions. - _Robert Israel_, Oct 23 2015
%p seq(3*n - 2*floor(sqrt(n))^2, n=0..1000); # _Robert Israel_, Oct 23 2015
%o (PARI) a(n) = 3*n - 2*sqrtint(n)^2; \\ _Michel Marcus_, Oct 23 2015
%Y Cf. A002061, A053186, A094766.
%K nonn
%O 0,3
%A _N. J. A. Sloane_, Jun 10 2004
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