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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

%I

%S 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,

%T 77,113,93,151,124,186,144,221,177,249,225,289,253,333,310,411,343,

%U 479,390,534,456,593,527,674,605,756,667,859,733,954,826,1049,936

%N 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.

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Integer_triangle">Integer Triangle</a>

%F 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.

%t 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}]

%Y Cf. A308216.

%K nonn

%O 1,7

%A _Wesley Ivan Hurt_, May 15 2019

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Last modified May 23 12:48 EDT 2022. Contains 353975 sequences. (Running on oeis4.)