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 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. 3
 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 (list; graph; refs; listen; history; text; internal format)
 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; od; fi; od; od; od; 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

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Last modified July 17 05:50 EDT 2024. Contains 374360 sequences. (Running on oeis4.)