%I M0586 N0212 #32 May 13 2022 18:49:36

%S 1,2,3,4,7,13,24,44,83,157,297,567,1085,2086,4019,7766,15039,29181,

%T 56717,110408,215225,420076,820836,1605587,3143562,6160098,12080946,

%U 23710229,46565965,91512121,179947985,354043613,696935548,1372589372

%N Landau's approximation to population of x^2 + y^2 <= 2^n.

%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 Sean A. Irvine, <a href="/A000690/b000690.txt">Table of n, a(n) for n = 0..999</a>

%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(n) = round(b*2^n/sqrt(log(2^n))) where b=0.764223654... is the Landau-Ramanujan constant (A064533).

%Y Cf. A000050, A064533.

%K nonn

%O 0,2

%A _N. J. A. Sloane_

%E More terms from _Sean A. Irvine_, Feb 23 2011

%E Name clarified by _Seth A. Troisi_, Apr 28 2022