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A101904 Number of leg-hypotenuse twin Pythagorean triples < 10^n. 0

%I

%S 1,6,21,70,223,706,2235,7070,22360,70710,223606,707106,2236067,

%T 7071067,22360679,70710677,223606797,707106780,2236067976,7071067811,

%U 22360679774,70710678118,223606797749,707106781186,2236067977499

%N Number of leg-hypotenuse twin Pythagorean triples < 10^n.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/TwinPythagoreanTriple.html">Twin Pythagorean Triple</a>

%e For a(2)=6 because {3, 4, 5}, {5, 12, 13}, {7, 24, 25}, {9, 40, 41}, {11, 60, 61}, {13, 84, 85}.

%t f[n_] := Round[ Sqrt[ (10^n - 1)/2] - 1]; Table[ f[n], {n, 25}] (* _Robert G. Wilson v_, Jan 08 2005 *)

%Y Cf. A095861, length of the longer leg in A046092, length of hypotenuse in A001844.

%K nonn

%O 1,2

%A _Eric W. Weisstein_, Dec 20 2004

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Last modified March 26 00:16 EDT 2019. Contains 321477 sequences. (Running on oeis4.)