%I #6 Mar 14 2015 17:21:06
%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