A000693 - OEIS

%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