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A270546 Denominators of r-Egyptian fraction expansion for sqrt(1/2), where r(k) = 1/(2k-1). 2
2, 2, 5, 325, 200533, 65627675599, 22975481891957121466348, 1958997403653886589078102754522745217186637162, 141280756113351994103874857935521871912536028357392961997286697261498102983722388787617517574 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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.

See A269993 for a guide to related sequences.

LINKS

Clark Kimberling, Table of n, a(n) for n = 1..12

Eric Weisstein's World of Mathematics, Egyptian Fraction

Index entries for sequences related to Egyptian fractions

EXAMPLE

sqrt(1/2) = 1/(1*2) + 1/(3*2) + 1/(5*5) + 1/(7*325) + ...

MATHEMATICA

r[k_] := 1/(2k-1); f[x_, 0] = x; z = 10;

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

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

x = Sqrt(1/2); Table[n[x, k], {k, 1, z}]

PROG

(PARI) r(k) = 1/(2*k-1);

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

a(k, x=sqrt(1/2)) = ceil(r(k)/f(k-1, x)); \\ Michel Marcus, Apr 03 2016

CROSSREFS

Cf. A269993, A005408, A010503.

Sequence in context: A036739 A158311 A158061 * A163119 A091085 A011144

Adjacent sequences:  A270543 A270544 A270545 * A270547 A270548 A270549

KEYWORD

nonn,frac,easy

AUTHOR

Clark Kimberling, Apr 02 2016

STATUS

approved

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Last modified January 23 19:12 EST 2020. Contains 331175 sequences. (Running on oeis4.)