A070085 - OEIS

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A070085

a(n) = A070080(n)^2 + A070081(n)^2 - A070082(n)^2.

1, 1, 4, 1, -1, 4, 1, -3, 9, 4, 2, 1, -5, -7, 9, 4, 0, 16, 1, -7, -11, 9, 7, 4, -2, -4, 16, 1, -9, -15, 9, -17, 5, 25, 4, -4, -8, 16, 14, 1, -11, -19, 9, -23, 3, 1, 25, 4, -6, -12, 16, -14, 12, 36, 1, -13, -23, 9, -29, 1, -31, -3, 25, 23, 4, -8

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

COMMENTS

The integer triangle [A070080(n)<=A070081(n)<=A070082(n)] is acute iff a(n)>0, right iff a(n)=0 and obtuse iff a(0)<0.

LINKS

Table of n, a(n) for n=1..66.

Eric Weisstein's World of Mathematics, Acute Triangle.

Eric Weisstein's World of Mathematics, Right Triangle.

Eric Weisstein's World of Mathematics, Obtuse Triangle.

R. Zumkeller, Integer-sided triangles

MATHEMATICA

maxPer = m = 22;

sides[per_] := Select[Reverse /@ IntegerPartitions[per, {3}, Range[Ceiling[ per/2]]], #[[1]] < per/2 && #[[2]] < per/2 && #[[3]] < per/2&];

triangles = DeleteCases[Table[sides[per], {per, 3, m}], {}] // Flatten[#, 1]& // SortBy[Total[#] m^3 + #[[1]] m^2 + #[[2]] m + #[[1]]&];

#[[1]]^2 + #[[2]]^2 - #[[3]]^2& /@ triangles (* Jean-François Alcover, Jul 31 2018 *)

CROSSREFS

Cf. A070093, A070101, A024155, A070118, A070127, A070136.

Sequence in context: A343408 A080278 A258328 * A131776 A010322 A299537

Adjacent sequences: A070082 A070083 A070084 * A070086 A070087 A070088

KEYWORD

sign

AUTHOR

Reinhard Zumkeller, May 05 2002

STATUS

approved