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A267803
Number of unit hexagonal lattice cells (hexagon in the origin) enclosed by origin centered circle of radius n.
0
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
1,3
COMMENTS
As n -> infinity, lim a(n)/(n^2) -> 2*Pi/(3*sqrt(3)).
CROSSREFS
Cf. A248897(2*Pi/(3*sqrt(3))).
Sequence in context: A172057 A173176 A216550 * A240971 A023255 A373584
KEYWORD
nonn,easy
AUTHOR
Luca Petrone, Jan 20 2016
STATUS
approved