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 A308452 Number of integer-sided triangles with perimeter n and side lengths a, b and c such that a <= b <= c, and b is prime. 0
 0, 0, 0, 0, 1, 1, 2, 1, 2, 1, 2, 1, 2, 2, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 5, 4, 6, 6, 8, 8, 10, 9, 11, 10, 12, 11, 14, 12, 14, 12, 14, 12, 14, 13, 16, 15, 18, 17, 20, 18, 20, 19, 21, 20, 22, 20, 22, 20, 22, 20, 23, 21, 24, 22, 25, 23, 26, 24, 26, 24, 26 (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)} sign(floor((i+k)/(n-i-k+1))) * A010051(i). MATHEMATICA Table[Sum[Sum[ (PrimePi[i] - PrimePi[i - 1]) Sign[Floor[(i + k)/(n - i - k + 1)]], {i, k, Floor[(n - k)/2]}], {k, Floor[n/3]}], {n, 100}] CROSSREFS Cf. A010051, A308451. Sequence in context: A161260 A161285 A235189 * A103682 A023134 A304536 Adjacent sequences: A308449 A308450 A308451 * A308453 A308454 A308455 KEYWORD nonn AUTHOR Wesley Ivan Hurt, May 27 2019 STATUS approved

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Last modified January 26 22:13 EST 2023. Contains 359836 sequences. (Running on oeis4.)