Number of n-length words w over a 4-ary alphabet such that w is empty or a prefix z concatenated with letter a_i and i=1 or 0 < #(z,a_{i-1}) >= #(z,a_i), where #(z,a_i) counts the occurrences of the i-th letter in z.
A240610
Number of n-length words w over a 4-ary alphabet such that w is empty or a prefix z concatenated with letter a_i and i=1 or 0 < #(z,a_{i-1}) >= #(z,a_i), where #(z,a_i) counts the occurrences of the i-th letter in z.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =5a(4) =14a(5) =45a(6) =149a(7) =509a(8) =1756a(9) =6082a(10) =21246a(11) =74125a(12) =260940a(13) =917060a(14) =3251573a(15) =11514563a(16) =41115372a(17) =146687475a(18) =527318119a(19) =1894548198a(20) =6853413645a(21) =24782205276a(22) =90165044683a(23) =327958242274
External references
- oeis: A240610