

A144229


The numerators of the convergents to the recursion x=1/(x^2+1).


1




OFFSET

0,3


COMMENTS

The recursion converges to the real root of 1/(x^2+1)  x = 0, 0.682327803...
An interesting consequence of this result occurs if we multiply by x^2+1 to get 1xx^3=0. These different equations intersect at the same root 0.682327803... Note also that a(n) is a square. The square roots form sequence A076725.
a(n) is the number of (0,1)labelled perfect binary trees of height n such that no adjacent nodes have 1 as the label and the root is labelled 0.  Ran Pan, May 22 2015


LINKS

Table of n, a(n) for n=0..8.
Ran Pan, Exercise R, Project P.


FORMULA

a(n+2) = (a(n)^2 + a(n+1))^2.  Ran Pan, May 22 2015
a(n) ~ c * d^(2^n), where c = A088559 = 0.465571231876768... is the root of the equation c*(1+c)^2 = 1, d = 1.6634583970724267140029... .  Vaclav Kotesovec, May 22 2015


MATHEMATICA

f[n_]:=(n+1/n)/n; Prepend[Denominator[NestList[f, 2, 7]], 1] (* Vladimir Joseph Stephan Orlovsky, Nov 19 2010 *)
RecurrenceTable[{a[n]==(a[n2]^2 + a[n1])^2, a[0]==1, a[1]==1}, a, {n, 0, 10}] (* Vaclav Kotesovec, May 22 2015 after Ran Pan *)


PROG

(PARI) x=0; for(j=1, 10, x=1/(x^2+1); print1((numerator(x))", "))


CROSSREFS

Cf. A076725, A088559.
Sequence in context: A072882 A014253 A132553 * A284106 A063802 A276266
Adjacent sequences: A144226 A144227 A144228 * A144230 A144231 A144232


KEYWORD

frac,nonn


AUTHOR

Cino Hilliard, Sep 15 2008


STATUS

approved



