A248042 Denominators of approximation to 2^(1/3) by Newton's method after n iterations.

1, 3, 72, 894348, 1703358734191174242

Offset

0,2

Comments

Numerators are given in A248041.

Links

Table of n, a(n) for n=0..4.

Eric Weisstein's World of Mathematics, Cube Root

Wikipedia, Cube Root

Formula

a(n) = y(n)/gcd(x(n),y(n))

where x(n) = 2*(A248041(n-1)^3*a(n-1)^2 + a(n-1)^5)

and y(n) = 3*A248041(n-1)^2*a(n-1)^3;

x(0) = y(0) = 1.

Example

Approximations to 2^(1/3):
n = 1:            4/3 = 1.33333...; error = 0.07341...
n = 2:          91/72 = 1.26388...; error = 0.00396...
n = 3: 1126819/894348 = 1.25993...; error = 0.00001...
...

Crossrefs

Cf. A002580, A248041.

Sequence in context: A135866 A307925 A006270 * A139888 A271628 A079594

Adjacent sequences: A248039 A248040 A248041 * A248043 A248044 A248045

Keyword

nonn,frac

Author

Kival Ngaokrajang, Jan 11 2015

Status

approved