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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A218480 Number of 3n-length 10-ary words, either empty or beginning with the first letter of the alphabet, that can be built by repeatedly inserting triples of identical letters into the initially empty word. 2
 1, 1, 28, 1027, 42850, 1929043, 91320022, 4480436836, 225785025802, 11617042380355, 607729841261560, 32227411217273515, 1728444323307664720, 93593058046710649012, 5109705135623767855960, 280954986758729989837624, 15544627425243191634814666 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS In general, column k of A213027 is (for k > 1) asymptotic to a(n) ~ 3^(3*n+1/2) * (k-1)^(n+1) / (sqrt(Pi) * (2*k-3)^2 * 4^n * n^(3/2)). - Vaclav Kotesovec, Aug 31 2014 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..200 FORMULA a(n) = 1/n * Sum_{j=0..n-1} C(3*n,j)*(n-j)*9^j for n>0, a(0) = 1. Recurrence: 2*n*(2*n-1)*(13*n-15)*a(n) = (55159*n^3 - 95963*n^2 + 38478*n - 1080)*a(n-1) - 27000*(3*n-5)*(3*n-4)*(13*n-2)*a(n-2). - Vaclav Kotesovec, Aug 31 2014 a(n) ~ 3^(5*n+5/2) / (289 * sqrt(Pi) * 4^n * n^(3/2)). - Vaclav Kotesovec, Aug 31 2014 MAPLE a:= n-> `if`(n=0, 1, add(binomial(3*n, j)*(n-j)*9^j, j=0..n-1)/n): seq(a(n), n=0..20); CROSSREFS Column k=10 of A213027. Sequence in context: A034904 A189995 A228689 * A162006 A025753 A160312 Adjacent sequences: A218477 A218478 A218479 * A218481 A218482 A218483 KEYWORD nonn AUTHOR Alois P. Heinz, Oct 29 2012 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 January 31 05:55 EST 2023. Contains 359947 sequences. (Running on oeis4.)