The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A128057 Expansion of (1+x)/sqrt(1+4x^2). 2
 1, 1, -2, -2, 6, 6, -20, -20, 70, 70, -252, -252, 924, 924, -3432, -3432, 12870, 12870, -48620, -48620, 184756, 184756, -705432, -705432, 2704156, 2704156, -10400600, -10400600, 40116600, 40116600, -155117520, -155117520 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Hankel transform is A128056. Binomial transform is A128058. Unsigned version is A128014. LINKS Table of n, a(n) for n=0..31. FORMULA a(n)=(-1)^C(n,2)*(C(n,n/2)*(1+(-1)^n)/2+C(n-1,(n-1)/2)*(1-(-1)^n)/2); Conjecture: n*(5*n-9)*a(n) +4*a(n-1) +4*(5*n-4)*(n-2)*a(n-2)=0. - R. J. Mathar, Dec 02 2014 D-finite with recurrence: n*a(n) +(n-2)*a(n-1) +4*(n-1)*a(n-2) +4*(n-3)*a(n-3)=0. - R. J. Mathar, Dec 02 2014 MATHEMATICA CoefficientList[Series[(1+x)/Sqrt[1+4x^2], {x, 0, 40}], x] (* Harvey P. Dale, May 12 2015 *) CROSSREFS Cf. A000984. Sequence in context: A071407 A309094 A109859 * A128014 A135401 A129881 Adjacent sequences: A128054 A128055 A128056 * A128058 A128059 A128060 KEYWORD easy,sign AUTHOR Paul Barry, Feb 13 2007 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 11 17:54 EDT 2024. Contains 375839 sequences. (Running on oeis4.)