A206771 0 followed by the numerators of the reduced (A001803(n) + A001790(n)) / (2*A046161(n)).

0, 1, 1, 9, 5, 175, 189, 1617, 429, 57915, 60775, 508079, 264537, 8788507, 9100525, 75218625, 9694845, 5109183315, 5250613995, 43106892675, 22090789875, 723694276305, 740104577355, 6049284520695, 1543768261425, 201547523019375

Offset

0,4

Comments

We write the fractions a(n)/b(n) and higher order differences as a matrix:

0, 1, 1, 9/8, 5/4,...

1, 0, 1/8, 1/8, 15/128,... = (A001790(n)/A046161(n) +Lorbeta(n)) /2

-1, 1/8, 0, -1/128, -1/128,... = (Lorbeta(n+1) +A161200(n+1)/A046161(n+1)) / 2

9/8, -1/8, -1/128, 0, 1/1024,...

-5/4, 15/128, 1/128, 1/1024, 0,...

Here, Lorbeta(0)=1 and Lorbeta(n) = -A098597(n-1)/A046161(n) for n>0 is the inverse of the Lorentz factor.

The first line with numerators a(n) and denominators b(n) is 0, 1, 1, 9/8, 5/4, 175/128, 189/128, 1617/1024, 429/256, 57915/32768, 60775/32768,... It is an autosequence: Its inverse binomial transform is the signed sequence.

a(n+1)/(2*n-1)= 1, 3, 1, 25, 21, 147, 33, 3861, 3575, 26741,... .

a(n+1)/A146535(n) = 9, 5, 35, 27, 539, 39, 4455,... .

A001790(n)/A046161(n) yields the coefficients of the Lorentz factor (or Lorentz gamma factor). With b for beta and g for gamma:

g = (1-b^2)^-1 = 1 + (b^2)/2 + 3*(b^4)/8 + 5*(b^6)/16 + ... .

b = (1-g^-2)^-1 = 1 - (g^-2)/2 - (g^-4)/8 - (g^-6)/16 - ... .

Are the denominators of the first subdiagonal 1, 1/8, -1/128, 1/1024,... A061549(n) ?

a(n+1)/(A000108(n)*b(n)) = 1, 1, 9/16, 1/4, 25/256, 9/256, 49/4096, 1/256, 81/65536, 25/65536, 121/1048576,... = A191871(n+1)/ A084623(n+1)^2 ?

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

OEIS Wiki, Autosequence

Wikipedia, Lorentz Factor.

Formula

a(n) = A000265(n) * A001790(n-1).

a(n) = A098597(n-1) * A191871(n). See also A181318

a(n) = numerator of n*binomial(2n-2,n-1)/4^(n-1). - Nathaniel Johnston, Dec 16 2022

Example

From the first formula: a(1)=1*1, a(2)=1*1, a(3)=3*3, a(4)=1*5, a(5)=5*35, a(6)=3*63.

Maple

A206771 := proc(n)
        A001790(n)+A001803(n) ;
        %/2/A046161(n) ;
        numer(%) ;
end proc: # R. J. Mathar, Jan 18 2013

Mathematica

max = 25; A001803 = CoefficientList[Series[(1 - x)^(-3/2), {x, 0, max}], x] // Numerator; A001790 = CoefficientList[Series[1/Sqrt[(1 - x)], {x, 0, max}], x] // Numerator; A046161 = Table[Binomial[2n, n]/4^n, {n, 0, max}] // Denominator; a[n_] := (A001803[[n]] + A001790[[n]])/(2*A046161[[n]]) // Numerator; a[0] = 0; Table[a[n], {n, 0, max}]
(* or (from 1st formula) : *) Table[ n*Numerator[4^(1-n)*Binomial[2n-2, n-1]]/2^IntegerExponent[n, 2], {n, 0, max}]
(* or (from 2nd formula) : *) Table[ Numerator[ CatalanNumber[n-1]/2^(2n-1)]*Numerator[n^2/2^n], {n, 0, max}] (* Jean-François Alcover, Jan 31 2013 *)

Prog

(Magma) /* By definition: */ m:=25; R<x>:=PowerSeriesRing(Rationals(), m); p:=Coefficients(R!(1/(1-x)^(1/2))); q:=Coefficients(R!((1-x)^(-3/2))); A001790:=[Numerator(p[i]): i in [1..m]]; A001803:=[Numerator(q[i]): i in [1..m]]; A046161:=[Denominator(Binomial(2*n, n)/4^n): n in [0..m-1]]; [0] cat [Numerator((A001803[n]+A001790[n])/(2*A046161[n])): n in [1..m]]; // Bruno Berselli, Mar 11 2013

Crossrefs

Cf. A187791, A000108.

Sequence in context: A248308 A035417 A038295 * A317869 A103362 A252245

Adjacent sequences: A206768 A206769 A206770 * A206772 A206773 A206774

Keyword

nonn,frac

Author

Paul Curtz, Jan 10 2013

Extensions

a(11)-a(25) from Jean-François Alcover, Jan 13 2013

Status

approved