A267803 Number of unit hexagonal lattice cells (hexagon in the origin) enclosed by origin centered circle of radius n.

1, 1, 7, 13, 19, 31, 43, 61, 85, 97, 121, 151, 175, 211, 241, 271, 313, 349, 385, 439, 499, 535, 583, 649, 691, 757, 823, 877, 955, 1027, 1087, 1159, 1249, 1321, 1401, 1483, 1561, 1663, 1765, 1827, 1945, 2053, 2133, 2233, 2347, 2443, 2563, 2677, 2779, 2905

Offset: 1

Author

Luca Petrone, Jan 20 2016

Keywords

• nonn
• easy
• changed

Links

• Nicolay Avilov, Illustration of the first terms

Crossrefs

Cf. A053458, A267710.

Cf. A248897 (2*Pi/(3*sqrt(3))).

Formula

Limit_{n->oo} a(n)/(n^2) = 2*Pi/(3*sqrt(3)).