A053456 Open disk numbers (version 1): a(n) is the number of points (i,j), i,j, integers, contained in an open disk of diameter n, centered at (0,0).

0, 1, 1, 9, 9, 21, 25, 37, 45, 69, 69, 97, 109, 137, 145, 177, 193, 225, 249, 293, 305, 349, 373, 421, 437, 489, 517, 577, 609, 665, 697, 749, 793, 861, 889, 973, 1005, 1085, 1125, 1201, 1245, 1313, 1369, 1457, 1513, 1597, 1649, 1741, 1789, 1885, 1941

Offset

0,4

Links

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

Formula

a(n)/(n/2)^2->Pi.

Crossrefs

Cf. A053411, A053457, A053458, A053459.

Bisections: A051132, A036704.

Cf. A000796 (Pi).

Sequence in context: A161365 A214831 A197497 * A144424 A359038 A282269

Adjacent sequences: A053453 A053454 A053455 * A053457 A053458 A053459

Keyword

easy,nonn

Author

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

Status

approved