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A053458 Open disk numbers (version 3): a(n)= number of points (i+j/2,j*sqrt(3)/2), i,j integers (triangular grid) contained in a open disk of diameter n, centered at (0,0). 2
0, 1, 1, 7, 13, 19, 31, 43, 55, 73, 85, 109, 121, 151, 169, 199, 235, 253, 295, 313, 361, 397, 433, 475, 511, 571, 595, 661, 703, 757, 817, 859, 925, 979, 1039, 1111, 1159, 1237, 1285, 1381, 1453, 1519, 1597, 1663, 1759, 1813, 1915, 1993, 2077, 2173, 2257 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

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

LINKS

Table of n, a(n) for n=0..50.

CROSSREFS

A053416, A053456-A053459.

Sequence in context: A091180 A272381 A242190 * A040058 A172057 A173176

Adjacent sequences:  A053455 A053456 A053457 * A053459 A053460 A053461

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified January 26 09:21 EST 2022. Contains 350597 sequences. (Running on oeis4.)