A000693 Related to population of numbers of form x^2 + y^2.
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
Keywords
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
- 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.
Extensions
More terms from Sean A. Irvine, Feb 24 2011