A164775 a(n) is the number of positive integers <= 10^n that can be expressed as a sum of two squares.

7, 43, 330, 2749, 24028, 216341, 1985459, 18457847, 173229058, 1637624156, 15570512744, 148736628858, 1426306930865, 13722217893214, 132387263219058, 1280309691127436

Offset

1,1

Links

Table of n, a(n) for n=1..16.

Peter Shiu, Counting Sums of Two Squares: The Meissel-Lehmer Method, Mathematics of Computation 47:175 (July 1986), pp. 351-360. [Beware errors.]

Eric Weisstein's World of Mathematics, Landau-Ramanujan Constant

Formula

a(n) = A180416(n) + ceiling(sqrt(10^n)). - Hiroaki Yamanouchi, Jul 14 2014

Example

a(1)=7 since 1 = 0^2 + 1^2, 2 = 1^2 + 1^2, 4 = 0^2 + 2^2, 5 = 1^2 + 2^2, 8 = 2^2 + 2^2, 9 = 0^2 + 3^2, 10 = 1^2 + 3^3.

Crossrefs

Cf. A000050, A001481, A064533, A227158, A275649, A275650.

Sequence in context: A331236 A042213 A193705 * A127999 A208595 A121675

Adjacent sequences: A164772 A164773 A164774 * A164776 A164777 A164778

Keyword

nonn,hard,more

Author

Eric W. Weisstein, Aug 26 2009

Extensions

Offset changed from 0 to 1 by Robert G. Wilson v, Aug 29 2009

a(9) from Eric W. Weisstein, Aug 29 2009

a(10) from Donovan Johnson, Sep 16 2009

a(11)-a(12) from Ant King, May 02 2010

a(11)-a(12) corrected and a(13)-a(16) added by Hiroaki Yamanouchi, Jul 14 2014

Status

approved