login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A053415 Circle numbers (version 3): a(n)= number of points (i,j), i,j integers, contained in a circle of diameter n, centered at (1/2,1/2). 10
0, 0, 4, 4, 12, 16, 32, 32, 52, 60, 80, 88, 112, 124, 156, 172, 208, 216, 256, 276, 316, 332, 384, 408, 448, 484, 540, 560, 616, 648, 716, 740, 812, 848, 912, 952, 1020, 1060, 1124, 1184, 1264, 1304, 1396, 1436, 1528, 1576, 1664, 1716, 1804, 1876, 1976 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

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

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

MATHEMATICA

cx = 1/2; cy = 1/2; a[n_] := Sum[ dj = 1/2*Sqrt[ Abs[n^2 - 4*cx^2 + 8*cx*i - 4*i^2]]; j1 = cy - dj // Floor; j2 = cy + dj // Ceiling; Sum[Boole[ (i - cx)^2 + (j - cy)^2 <= n^2/4], {j, j1, j2}], {i, cx - n/2 // Floor, cx + n/2 // Ceiling}]; Table[a[n], {n, 0, 50}] (* Jean-Fran├žois Alcover, Jun 06 2013 *)

CROSSREFS

Cf. A053411, A053414, A053415, A053416, A053417.

Sequence in context: A121189 A136485 A157617 * A303315 A331606 A079902

Adjacent sequences:  A053412 A053413 A053414 * A053416 A053417 A053418

KEYWORD

easy,nonn

AUTHOR

Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Jan 10 2000

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 19 17:03 EDT 2021. Contains 347564 sequences. (Running on oeis4.)