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A024361 Number of primitive Pythagorean triangles with leg n. 7
0, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 2, 1, 0, 2, 1, 1, 0, 1, 2, 2, 0, 1, 2, 1, 0, 1, 2, 1, 0, 1, 1, 2, 0, 2, 2, 1, 0, 2, 2, 1, 0, 1, 2, 2, 0, 1, 2, 1, 0, 2, 2, 1, 0, 2, 2, 2, 0, 1, 4, 1, 0, 2, 1, 2, 0, 1, 2, 2, 0, 1, 2, 1, 0, 2, 2, 2, 0, 1, 2, 1, 0, 1, 4, 2, 0, 2, 2, 1, 0, 2, 2, 2, 0, 2, 2, 1, 0, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,12

COMMENTS

Consider primitive Pythagorean triangles (A^2 + B^2 = C^2, (A, B) = 1, A <= B); sequence gives number of times A or B takes value n.

For n>1, a(n)=0 for n=A016825=2(mod 4).

LINKS

Table of n, a(n) for n=1..99.

Ron Knott, Pythagorean Triples and Online Calculators

Eric Weisstein's World of Mathematics, Pythagorean Triple

EXAMPLE

a(12)=2 because 12 appears twice, in (A,B,C) = (5,12,13) and (12,35,37).

MATHEMATICA

Table[If[n == 1 || Mod[n, 4] == 2, 0, 2^(Length[FactorInteger[n]] - 1)], {n, 100}]

CROSSREFS

Cf. A024362, A046079, A020883, A020884.

Sequence in context: A096419 A283616 A130182 * A190676 A135486 A030187

Adjacent sequences:  A024358 A024359 A024360 * A024362 A024363 A024364

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

Incorrect comment removed by Ant King, Jan 28 2011

STATUS

approved

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Last modified September 26 01:25 EDT 2017. Contains 292500 sequences.