This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A176006 The number of branching configurations of RNA (see Sankoff, 1985) with n or fewer hairpins. 1
 1, 2, 4, 10, 32, 122, 516, 2322, 10880, 52466, 258564, 1296282, 6589728, 33887466, 175966212, 921353250, 4858956288, 25786112994, 137604139012, 737922992938, 3974647310112, 21493266631002, 116642921832964, 635074797251890 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 Guo-Niu Han, Enumeration of Standard Puzzles Guo-Niu Han, Enumeration of Standard Puzzles [Cached copy] Sankoff (1985) Simultaneous solution of the RNA folding, alignment and protosequence problems, Siam J. Appl. Math 45(5):810-825. FORMULA G.f.: (3-x-sqrt(1-6*x+x^2))/(2*(1-x)). Conjecture : n*a(n) +(9-7*n)*a(n-1) +(7*n-12)*a(n-2) +(3-n)*a(n-3)=0. - R. J. Mathar, Jul 24 2012 a(n) ~ 2^(1/4)*(3+2*sqrt(2))^n/(4*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, Oct 20 2012 EXAMPLE For n = 3, the a(3) = 10 branching configurations with 3 or fewer hairpins are: unfolded, (), ()(), (()()), ()()(), (()())(), ()(()()), (()()()), ((()())()), and (()(()())). MATHEMATICA CoefficientList[Series[(3-x-Sqrt[1-6*x+x^2])/(2*(1-x)), {x, 0, 20}], x] (* Vaclav Kotesovec, Oct 20 2012 *) PROG (PARI) x='x+O('x^50); Vec((3-x-sqrt(1-6*x+x^2))/(2*(1-x))) \\ G. C. Greubel, Mar 22 2017 CROSSREFS The cumulative sums of A155069. Sequence in context: A120017 A000736 A263663 * A263664 A263665 A001250 Adjacent sequences:  A176003 A176004 A176005 * A176007 A176008 A176009 KEYWORD easy,nonn AUTHOR Lee A. Newberg, Apr 05 2010 STATUS approved

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

Last modified January 18 13:09 EST 2019. Contains 319271 sequences. (Running on oeis4.)