about A001333, A034183, A000129 (Pell numbers)
vdmcc
w.meeussen.vdmcc at vandemoortele.be
Thu Apr 1 19:00:07 CEST 1999
about
A001333 1,1,3,7,17,41,99,239,577,1393
A034183 1,3,7,17,41,99,239,577,1393
A000129 0,1,2,5,12,29,70,169,408,985
A024542 1,2,5,12,29, ... now dead, deceased, gone, ... !
they are linked by the definition
"(denominators of continued fraction convergents to sqrt(2))."
f(n) = 2*f(n-1)+f(n-2), f(0)=0, f(1)=1;
nothing new, except maybe :
A001333(n)+A001333(n+1) = 2 A000129(n+1)
A000129(n)+A000129(n+1) = A001333(n+1)
and working out the recursion gives :
A001333(n) = ( (1-Sqrt[2])^n + (1+Sqrt[2])^n) /2
A000129(n) = (-(1-Sqrt[2])^n + (1+Sqrt[2])^n) /2/Sqrt[2]
-------------------------------------------------------------
we meet these sequences pair-wise in :
NestList[1+1/(#+1 )&,m,3]
=
1 1 1
{m, 1 + -----, 1 + ---------, 1 + -------------, ... }
1 + m 1 1
2 + ----- 2 + ---------
1 + m 1
2 + -----
1 + m
=
2 + m 4 + 3 m 10 + 7 m 24 + 17 m 58 + 41 m 140 + 99 m 338 + 239 m
{m, -----, -------, --------, ---------, ---------, ----------, -----------}
1 + m 3 + 2 m 7 + 5 m 17 + 12 m 41 + 29 m 99 + 70 m 239 + 169 m
with m -> 0 :
{0, 2, 4/3, 10/7, 24/17, 58/41, 140/99, 338/239}
numerator = 2 A000129(n) ; denominator = A001333(n)
and with m -> 1 :
{1, 3/2, 7/5, 17/12, 41/29, 99/70, 239/169, 577/408}
numerator = A001333(n+1) ; denominator = A000129(n+1)
so, the above sequence of rationals in m is :
( 2 a000129[n]+a001333[n] m)/(a001333[n]+a000129[n] m)
we could call this thing "the n-th iterate of function f: x -> 1+1/(x+1) on
m"
or (f^n)(m) for short.
with of course:
Limit[a001333[n]/a000129[n],n->oo] = Sqrt[2]
and
Limit[a000129[n+1]/a000129[n],n->oo] = Limit[a001333[n+1]/a001333[n],n->oo]
= 1+Sqrt[2]
as I said, nothing new,
w.meeussen.vdmcc at vandemoortele.be
tel +32 (0) 51 33 21 11
fax +32 (0) 51 33 21 75
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