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 A308225 Take the integer-sided triangles with perimeter n and mutually coprime sides a, b and c such that a <= b <= c. a(n) is the sum of all the b's. 0
 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 5, 5, 0, 13, 0, 14, 7, 8, 7, 42, 9, 17, 29, 49, 20, 87, 11, 59, 22, 57, 37, 153, 24, 94, 82, 171, 58, 239, 62, 185, 79, 184, 81, 384, 106, 283, 163, 333, 91, 484, 156, 400, 181, 365, 166, 840, 218, 479, 385, 660, 280 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,12 LINKS Wikipedia, Integer Triangle FORMULA a(n) = Sum_{k=1..floor(n/3)} Sum_{i=k..floor((n-k)/2)} sign(floor((i+k)/(n-i-k+1))) * [gcd(i,k) * gcd(i,n-i-k) * gcd(k,n-i-k) = 1] * i, where [] is the Iverson Bracket. MATHEMATICA Table[Sum[Sum[i*Floor[1/(GCD[i, k]*GCD[i, n - i - k]*GCD[k, n - i - k])]*Sign[Floor[(i + k)/(n - i - k + 1)]], {i, k, Floor[(n - k)/2]}], {k, Floor[n/3]}], {n, 100}] CROSSREFS Cf. A308224. Sequence in context: A005397 A259124 A273515 * A021718 A193108 A212044 Adjacent sequences:  A308222 A308223 A308224 * A308226 A308227 A308228 KEYWORD nonn AUTHOR Wesley Ivan Hurt, May 16 2019 STATUS approved

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Last modified December 4 09:43 EST 2021. Contains 349485 sequences. (Running on oeis4.)