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 A101931 Number of primitive Pythagorean triples with hypotenuse < 10^n. 12
 1, 16, 158, 1593, 15919, 159139, 1591579, 15915492, 159154994, 1591549475, 15915494180, 159154943063, 1591549430580, 15915494309496, 159154943089963, 1591549430916326, 15915494309190251, 159154943091887752, 1591549430918979115 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The ratio a(n)/10^n as n->inf is 1/(2*Pi) = 0.15915... (Lehmer). - Tito Piezas III, Aug 11 2006 LINKS Hiroaki Yamanouchi, Table of n, a(n) for n = 1..21 D. N. Lehmer, Asymptotic evaluation of certain totient sums, Amer. J. Math. 22, 293-335, 1900. Eric Weisstein's World of Mathematics, Pythagorean Triple EXAMPLE a(1)=1 because there is one primitive solution (a,b,c) as (3,4,5) with c<10^1. PROG (PARI) a(n)=my(t, lim=10^n); for(m=2, sqrtint(lim-1), forstep(n=1+m%2, min(sqrtint(lim-m^2), m-1), 2, if(gcd(m, n)==1, t++))); t \\ Charles R Greathouse IV, Sep 13 2012 CROSSREFS Cf. A101929, A101930. Sequence in context: A320548 A211831 A036973 * A220630 A041005 A180798 Adjacent sequences:  A101928 A101929 A101930 * A101932 A101933 A101934 KEYWORD nonn AUTHOR Eric W. Weisstein, Dec 21 2004 EXTENSIONS More terms from Jan Feitsma and Bart Dopheide (dopheide(AT)fmf.nl), Mar 10 2005 a(10)-a(11) from Charles R Greathouse IV, Sep 14 2012 a(12) from Charles R Greathouse IV, Oct 15 2012 a(13)-a(19) from Hiroaki Yamanouchi, Jul 14 2014 STATUS approved

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Last modified September 30 15:55 EDT 2020. Contains 337439 sequences. (Running on oeis4.)