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%I M0767 N0292 #21 Feb 01 2022 01:09:59
%S 1,2,3,6,10,19,35,62,118,219,414,783,1497,2860,5503,10593,20471,39637,
%T 76918,149501,291115,567581,1108022,2165621,4237085,8297727,16264207,
%U 31904254,62630372,123031586,241837446,475647114,936020000,1842925873
%N Related to population of numbers of form x^2 + y^2.
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1964-0159174-9">The second-order term in the asymptotic expansion of B(x)</a>, Mathematics of Computation 18 (1964), pp. 75-86.
%H <a href="/index/Qua#quadpop">Index entries for sequences related to populations of quadratic forms</a>
%F a(1)=1, a(2)=2, a(n) = A000074(n) + a(n-2) for n > 2.
%K nonn
%O 1,2
%A _N. J. A. Sloane_
%E More terms from _Sean A. Irvine_, Feb 24 2011