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 A308157 Sum of the perimeters of all integer-sided obtuse triangles with perimeter n. 1

%I

%S 0,0,0,0,0,0,7,0,9,0,22,0,26,28,45,32,51,54,95,60,147,88,184,120,225,

%T 182,270,224,319,270,434,352,528,408,630,504,703,646,819,720,943,882,

%U 1161,968,1350,1104,1504,1296,1666,1500,1887,1716,2120,1890,2420

%N Sum of the perimeters of all integer-sided obtuse triangles with perimeter n.

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

%F a(n) = n * A070101(n).

%F a(n) = 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))).

%t Table[n*Sum[Sum[ (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. A070101.

%K nonn

%O 1,7

%A _Wesley Ivan Hurt_, May 14 2019

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Last modified September 23 20:42 EDT 2021. Contains 347617 sequences. (Running on oeis4.)