This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A206701 The number of words of length n created with the letters a,b,c with at least as many a's as b's and at least as many b's as c's and no adjacent letters forming the pattern aba and no subwords (any non adjacent subsequence of letters) of the form cbc. 2
 1, 1, 3, 9, 17, 46, 114, 262, 574, 1427, 2927, 6603, 14404, 30565, 63613, 138813, 280318, 587475, 1218642, 2483850, 5029611, 10412477, 20733046, 42016631, 84910771, 169447050, 337521488, 680231390, 1340806837, 2667729672, 5306731496, 10458274889, 20608397551 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..200 EXAMPLE a(0) = 1: "". a(1) = 1: "a". a(2) = 3: "aa", "ab", "ba". a(3) = 9: "aaa", "aab", "abc", "acb", "baa", "bac", "bca", "cab", "cba". MAPLE a:= n-> add (add (w (na, nb, n-na-nb, 0, 0),         nb=ceil((n-na)/2)..min(n-na, na)), na=ceil(n/3)..n): w:= proc(a, b, c, x, y) option remember;       `if`([a, b, c]=[0\$3], 1, `if`(a>0 and x<>2, w(a-1, b, c, 1, y), 0)+       `if`(b>0, w(a, b-1, c, `if`(x=1, 2, 0), `if`(y>0, 2, 0)), 0)+       `if`(c>0 and y<>2, w(a, b, c-1, 0, 1), 0))     end: seq (a(n), n=0..40);  # Alois P. Heinz, May 21 2012 PROG sage:  def myavoids(w): ....:  v = w.count(2) ....:  if w.count(1)

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .