|
|
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
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,7
|
|
LINKS
|
|
|
FORMULA
|
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
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|