A372218 - OEIS

A372218

a(n) is the number of ways to select three distinct points of an n X n grid forming a triangle whose sides do not pass through a grid point.

0, 4, 36, 184, 592, 1828, 4164, 9360, 18592, 34948, 59636, 102096, 161496, 255700, 385292, 562336, 796344, 1131996, 1552780, 2133368, 2855632, 3765492, 4876444, 6328104, 8049744, 10203820, 12766508, 15870744, 19496392, 23984444, 29090340, 35318968, 42535496, 50936036

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OFFSET

0,2

COMMENTS

a(n) is 1/6 of the number of ways to select three points (x,y), (u,v), (p,q) with gcd(x-u,y-v) = gcd(u-p,v-q) = gcd(p-x,q-y) = 1 and 0 <= x, y, u, v, p, q <= n in an n X n grid.

LINKS

Table of n, a(n) for n=0..33.

Felix Huber, Illustration of a(2)

EXAMPLE

See the linked illustration: a(2) = 36 because there are 36 ways to select three distinct points in a square grid with side length n that satisfy the condition.

MAPLE

A372218:=proc(n)

local x, y, u, v, p, q, a;

a:=0;

for x from 0 to n do

for y from 0 to n do

for u from 0 to n do

for v from 0 to n do

if gcd(x-u, y-v)=1 then

for p from 0 to n do

for q from 0 to n do

if gcd(x-p, y-q)=1 and gcd(p-u, q-v)=1 then a:=a+1 fi;

od;

fi;

od;

a:=a/6;

return a;

end proc;

seq(A372218(n), n=0..33);

CROSSREFS

Cf. A115004, A141224, A141255, A320540, A320541, A320544, A372217.

Sequence in context: A370660 A276295 A272146 * A034569 A270084 A272222

Adjacent sequences: A372215 A372216 A372217 * A372219 A372220 A372221

KEYWORD

nonn

AUTHOR

Felix Huber, Apr 28 2024

STATUS

approved