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A224212 Number of nonnegative solutions to x^2 + y^2 <= n. 4
1, 3, 4, 4, 6, 8, 8, 8, 9, 11, 13, 13, 13, 15, 15, 15, 17, 19, 20, 20, 22, 22, 22, 22, 22, 26, 28, 28, 28, 30, 30, 30, 31, 31, 33, 33, 35, 37, 37, 37, 39, 41, 41, 41, 41, 43, 43, 43, 43, 45, 48, 48, 50, 52, 52, 52, 52, 52, 54, 54, 54, 56, 56, 56, 58, 62, 62, 62, 64 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Seiichi Manyama, Table of n, a(n) for n = 0..1000

FORMULA

G.f.: (1/(1 - x))*(Sum_{k>=0} x^(k^2))^2. - Ilya Gutkovskiy, Mar 14 2017

MATHEMATICA

nn = 68; t = Table[0, {nn}]; Do[d = x^2 + y^2; If[0 < d <= nn, t[[d]]++], {x, 0, nn}, {y, 0, nn}]; Accumulate[Join[{1}, t]] (* T. D. Noe, Apr 01 2013 *)

PROG

(Python)

for n in range(99):

  k = 0

  for x in range(99):

    s = x*x

    if s>n: break

    for y in range(99):

        sy = s + y*y

        if sy>n: break

        k+=1

  print str(k)+', ',

CROSSREFS

Cf. A000925 (first differences).

Cf. A000606 (number of nonnegative solutions to x^2 + y^2 + z^2 <= n).

Cf. A057655 (number of integer solutions to x^2 + y^2 <= n).

Sequence in context: A100478 A112376 A161359 * A078490 A282847 A047877

Adjacent sequences:  A224209 A224210 A224211 * A224213 A224214 A224215

KEYWORD

nonn

AUTHOR

Alex Ratushnyak, Apr 01 2013

STATUS

approved

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Last modified January 23 10:45 EST 2020. Contains 331171 sequences. (Running on oeis4.)