login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A078928 Smallest p for which there are exactly n primitive Pythagorean triangles with perimeter p; i.e., smallest p such that A070109(p) = n. 2
12, 1716, 14280, 317460, 1542684, 6240360, 19399380, 63303240, 239168580, 397687290, 458948490, 813632820, 562582020, 2824441620, 3346393050, 6915878970, 6469693230, 8720021310, 9146807670, 8254436190, 23065862820, 25859373540, 202536455550 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A Pythagorean triangle is a right triangle whose edge lengths are all integers; such a triangle is 'primitive' if the lengths are relatively prime.

Least perimeter common to exactly n primitive Pythagorean triangles. - Lekraj Beedassy, May 14 2004

LINKS

Derek J. C. Radden and Peter T. C. Radden, Table of n, a(n) for n=1..39 (terms 1 through 15 were computed by Derek J. C. Radden)

C. B. T. (Reviewer), Review of Andrew S. Anema, A table of primitive Pythagorean triangle with identical perimeters, Mathematical Tables and Other Aids to Computation, Vol. 10, No. 53 (Jan., 1956), pp. 35-36.

EXAMPLE

a(2)=1716; the primitive Pythagorean triangles with edge lengths (364, 627, 725) and (195, 748, 773) both have perimeter 1716.

MATHEMATICA

oddpart[n_] := If[OddQ[n], n, oddpart[n/2]]; ct[p_] := Length[Select[Divisors[oddpart[p/2]], p/2<#^2<p&&GCD[ #, p/2/# ]==1&]]; a[n_] := For[per=2, True, per+=2, If[ct[per]==n, Return[per]]]

CROSSREFS

a(n) = 2*A078927(n). Cf. A070109.

Sequence in context: A034280 A146201 A009120 * A202968 A013717 A252767

Adjacent sequences:  A078925 A078926 A078927 * A078929 A078930 A078931

KEYWORD

nonn

AUTHOR

Dean Hickerson, Dec 15 2002

EXTENSIONS

a(8) from Robert G. Wilson v, Dec 19 2002

a(9)-a(15) from Derek J C Radden, Dec 22 2012

a(16)-a(39) from Peter T. C. Radden, Dec 29 2012

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 24 17:09 EDT 2020. Contains 337321 sequences. (Running on oeis4.)