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 A308218 Take the integer-sided obtuse triangles with perimeter n and sides a, b and c such that a <= b <= c. a(n) is the sum of all the b's. 0
 0, 0, 0, 0, 0, 0, 2, 0, 3, 0, 7, 0, 9, 9, 15, 11, 18, 18, 32, 21, 51, 30, 64, 41, 79, 62, 95, 77, 113, 93, 151, 124, 186, 144, 221, 177, 249, 225, 289, 253, 333, 310, 411, 343, 479, 390, 534, 456, 593, 527, 674, 605, 756, 667, 859, 733, 954, 826, 1049, 936 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,7 LINKS Wikipedia, Integer Triangle FORMULA a(n) = Sum_{k=1..floor(n/3)} Sum_{i=k..floor((n-k)/2)} (1-sign(floor((i^2 + k^2)/(n-i-k)^2))) * sign(floor((i+k)/(n-i-k+1))) i. MATHEMATICA Table[Sum[Sum[i (1 - Sign[Floor[(i^2 + k^2)/(n - i - k)^2]]) Sign[Floor[(i + k)/(n - i - k + 1)]], {i, k, Floor[(n - k)/2]}], {k, Floor[n/3]}], {n, 100}] CROSSREFS Cf. A308216. Sequence in context: A076563 A163974 A317443 * A067165 A079981 A117776 Adjacent sequences:  A308215 A308216 A308217 * A308219 A308220 A308221 KEYWORD nonn AUTHOR Wesley Ivan Hurt, May 15 2019 STATUS approved

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Last modified January 18 06:03 EST 2022. Contains 350438 sequences. (Running on oeis4.)