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 A020884 Ordered short legs of primitive Pythagorean triangles. 42
 3, 5, 7, 8, 9, 11, 12, 13, 15, 16, 17, 19, 20, 20, 21, 23, 24, 25, 27, 28, 28, 29, 31, 32, 33, 33, 35, 36, 36, 37, 39, 39, 40, 41, 43, 44, 44, 45, 47, 48, 48, 49, 51, 51, 52, 52, 53, 55, 56, 57, 57, 59, 60, 60, 60, 61, 63, 64, 65, 65, 67, 68, 68, 69, 69, 71, 72, 73, 75, 75, 76, 76, 77 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Consider primitive Pythagorean triangles (A^2 + B^2 = C^2, (A, B) = 1, A <= B); sequence gives values of A, sorted. Union of A081874 and A081925. - Lekraj Beedassy, Jul 28 2006 Each term in this sequence is given by f(m,n) = m^2 - n^2 or g(m,n) = 2mn where m and n are relatively prime positive integers with m > n, m and n not both odd. For example, a(1) = f(2,1) = 2^2 - 1^2 = 3 and a(4) = g(4,1) = 2*4*1 = 8. - Agola Kisira Odero, Apr 29 2016 All powers of 2 greater than 4 (2^2) are terms, and are generated by the function g(m,n) = 2mn. - Torlach Rush, Nov 08 2019 LINKS Ray Chandler, Table of n, a(n) for n = 1..10000 (first 1000 terms from Reinhard Zumkeller) P. Alfeld, Pythagorean Triples (broken link) Nick Exner, Generating Pythagorean Triples. This was originally a Java applet (1998), modified by Michael McKelvey in 2001 and redone as an HTML page with JavaScript by Evan Ramos in 2014. W. A. Kehowski, Pythagorean Triples (broken link) Ron Knott, Pythagorean Triples and Online Calculators MATHEMATICA shortLegs = {}; amx = 99; Do[For[b = a + 1, b < (a^2/2), c = (a^2 + b^2)^(1/2); If[c == IntegerPart[c] && GCD[a, b, c] == 1, AppendTo[shortLegs, a]]; b = b + 2], {a, 3, amx}]; shortLegs (* Vladimir Joseph Stephan Orlovsky, Aug 07 2008 *) PROG (Haskell) a020884 n = a020884_list !! (n-1) a020884_list = f 1 1 where    f u v | v > uu `div` 2        = f (u + 1) (u + 2)          | gcd u v > 1 || w == 0 = f u (v + 2)          | otherwise             = u : f u (v + 2)          where uu = u ^ 2; w = a037213 (uu + v ^ 2) -- Reinhard Zumkeller, Nov 09 2012 CROSSREFS Cf. A009004, A020882, A020883, A020885, A020886. Different from A024352. Cf. A024359 (gives the number of times n occurs). Cf. A037213. Sequence in context: A025050 A196115 A025051 * A183855 A024352 A288525 Adjacent sequences:  A020881 A020882 A020883 * A020885 A020886 A020887 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS Extended and corrected by David W. Wilson STATUS approved

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Last modified July 16 13:35 EDT 2020. Contains 335788 sequences. (Running on oeis4.)