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URL: https://oeis.org/A308157

⇱ A308157 - OEIS

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A308157
Sum of the perimeters of all integer-sided obtuse triangles with perimeter n.
1
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, 182, 270, 224, 319, 270, 434, 352, 528, 408, 630, 504, 703, 646, 819, 720, 943, 882, 1161, 968, 1350, 1104, 1504, 1296, 1666, 1500, 1887, 1716, 2120, 1890, 2420
OFFSET
1,7
FORMULA
a(n) = n * A070101(n).
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))).
MATHEMATICA
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}]
CROSSREFS
Cf. A070101.
Sequence in context: A213186 A296482 A272429 * A198555 A378124 A234355
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, May 14 2019
STATUS
approved