A053459 Open disk numbers (version 4): a(n) is the number of points (i+j/2,j*sqrt(3)/2), i,j integers (triangular grid) contained in an open disk of diameter n, centered at (1/2,0).

0, 0, 4, 8, 14, 22, 30, 42, 60, 74, 92, 108, 130, 148, 178, 206, 230, 262, 288, 324, 364, 400, 442, 480, 522, 562, 614, 662, 712, 764, 812, 868, 922, 988, 1050, 1106, 1176, 1234, 1312, 1376, 1452, 1528, 1598, 1678, 1750, 1838, 1920, 2006, 2092, 2172, 2266

Offset: 0

Author

Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Jan 13 2000

Keywords

• easy
• nonn

Comments

a(n)/(n/2)^2 -> Pi*2/sqrt(3).

Crossrefs

Cf. A053417, A053456, A053457, A053458.