A000693 Related to population of numbers of form x^2 + y^2. (Formerly M0767 N0292)

1, 2, 3, 6, 10, 19, 35, 62, 118, 219, 414, 783, 1497, 2860, 5503, 10593, 20471, 39637, 76918, 149501, 291115, 567581, 1108022, 2165621, 4237085, 8297727, 16264207, 31904254, 62630372, 123031586, 241837446, 475647114, 936020000, 1842925873

Offset

1,2

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

Table of n, a(n) for n=1..34.

D. Shanks, The second-order term in the asymptotic expansion of B(x), Mathematics of Computation 18 (1964), pp. 75-86.

Index entries for sequences related to populations of quadratic forms

Formula

a(1)=1, a(2)=2, a(n) = A000074(n) + a(n-2) for n > 2.

Crossrefs

Sequence in context: A368279 A374631 A123916 * A054178 A005833 A247162

Adjacent sequences: A000690 A000691 A000692 * A000694 A000695 A000696

Keyword

nonn

Author

N. J. A. Sloane

Extensions

More terms from Sean A. Irvine, Feb 24 2011

Status

approved