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A047809 a(n) counts different values of i^2+j^2+k^2 <= n^2 or number of distances from the origin to all integer points inside a sphere of radius n. 2
1, 2, 5, 9, 15, 23, 32, 43, 55, 70, 86, 103, 122, 143, 166, 190, 215, 243, 273, 304, 336, 371, 406, 443, 482, 523, 566, 611, 656, 704, 753, 803, 855, 910, 966, 1024, 1083, 1145, 1207, 1270, 1336, 1404, 1474, 1544, 1616, 1690, 1766, 1843, 1922, 2004 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

T. D. Noe, Table of n, a(n) for n = 0..1000

FORMULA

a(n) = number of b(i) <= n^2, b() = A000378.

MATHEMATICA

Table[ Length@Union@Flatten@Table[ i^2+j^2+k^2, {i, 0, n}, {j, 0, Min[ i, Floor[ Sqrt[ n^2-i^2 ] ] ]}, {k, 0, Min[ j, Floor[ Sqrt[ n^2-i^2-j^2 ] ] ]} ], {n, 0, 64} ]

CROSSREFS

Cf. A047808, A000378.

Sequence in context: A007982 A011904 A218914 * A014126 A019450 A098169

Adjacent sequences:  A047806 A047807 A047808 * A047810 A047811 A047812

KEYWORD

nonn,easy,nice

AUTHOR

Wouter Meeussen,David W. Wilson

STATUS

approved

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Last modified September 24 22:27 EDT 2018. Contains 315360 sequences. (Running on oeis4.)