

A000690


Landau's approximation to population of x^2 + y^2.
(Formerly M0586 N0212)


2



1, 2, 3, 4, 7, 13, 24, 44, 83, 157, 297, 567, 1085, 2086, 4019, 7766, 15039, 29181, 56717, 110408, 215225, 420076, 820836, 1605587, 3143562, 6160098, 12080946, 23710229, 46565965, 91512121, 179947985, 354043613, 696935548, 1372589372
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OFFSET

0,2


REFERENCES

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Sean A. Irvine, Table of n, a(n) for n = 0..999
D. Shanks, The secondorder term in the asymptotic expansion of B(x), Mathematics of Computation 18 (1964), pp. 7586.
Index entries for sequences related to populations of quadratic forms


FORMULA

a(n) = round(b*2^n/sqrt(log(2^n))) where b=0.764223654... is the LandauRamanujan constant (A064533).


CROSSREFS

Cf. A064533.
Sequence in context: A137495 A099779 A270440 * A049876 A049795 A014251
Adjacent sequences: A000687 A000688 A000689 * A000691 A000692 A000693


KEYWORD

nonn


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms from Sean A. Irvine, Feb 23 2011


STATUS

approved



