A270352 - OEIS

%I #15 Feb 24 2018 10:11:29

%S 4,8,44,977,498723,138012074956,45087947486104434546449,

%T 2223745971024423874814212532278502253766982404,

%U 3439676840537267257806008796995789895364959784333600339427716437786254731225969490712842205

%N Denominators of r-Egyptian fraction expansion for 1/Pi, where r = (1, 1/2, 1/4, 1/8, ...)

%C Suppose that r is a sequence of rational numbers r(k) <= 1 for k >= 1, and that x is an irrational number in (0,1).  Let f(0) = x, n(k) = floor(r(k)/f(k-1)), and f(k) = f(k-1) - r(k)/n(k).  Then x = r(1)/n(1) + r(2)/n(2) + r(3)/n(3) + ..., the r-Egyptian fraction for x.

%C See A269993 for a guide to related sequences.

%H Clark Kimberling, <a href="/A270352/b270352.txt">Table of n, a(n) for n = 1..11</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/EgyptianFraction.html">Egyptian Fraction</a>

%H <a href="/index/Ed#Egypt">Index entries for sequences related to Egyptian fractions</a>

%e 1/Pi = 1/4 + 1/(2*8) + 1/(4*44) + ...

%t r[k_] := 2/2^k; f[x_, 0] = x; z = 10;

%t n[x_, k_] := n[x, k] = Ceiling[r[k]/f[x, k - 1]]

%t f[x_, k_] := f[x, k] = f[x, k - 1] - r[k]/n[x, k]

%t x = 1/Pi; Table[n[x, k], {k, 1, z}]

%o (PARI) r(k) = 2/2^k;

%o f(k,x) = if (k==0, x, f(k-1, x) - r(k)/a(k, x););

%o a(k, x=1/Pi) = ceil(r(k)/f(k-1, x)); \\ _Michel Marcus_, Mar 18 2016

%Y Cf. A269993.

%K nonn,frac,easy

%O 1,1

%A _Clark Kimberling_, Mar 17 2016