A211339 - OEIS

A211339

Number of integer pairs (x,y) such that 1 < x <= y <= n and x^2 + y^2 <= n.

0, 1, 1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 5, 5, 5, 5, 6, 7, 7, 8, 8, 8, 8, 8, 9, 10, 10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 14, 14, 15, 16, 16, 16, 16, 17, 17, 17, 17, 17, 19, 19, 20, 21, 21, 21, 21, 21, 22, 22, 22, 23, 23, 23, 23, 25, 25, 25, 26, 26, 26, 26, 27, 28, 29

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OFFSET

1,5

COMMENTS

Partial sums of A025426.

For a guide to related sequences, see A211266.

LINKS

Table of n, a(n) for n=1..74.

FORMULA

a(n) = -1/2(-1 + floor(sqrt(n/2)))(floor(sqrt(n/2))) + Sum_{k=1..floor(sqrt(n/2))} floor(sqrt(n - k^2)). - Nicholas Stearns, Apr 03 2017

MATHEMATICA

a = 1; b = n; z1 = 120;