Number of words w of length n such that each letter of the quaternary alphabet is used at least once and for every prefix z of w we have #(z,a_i) = 0 or #(z,a_i) >= #(z,a_j) for all j>i and #(z,a_i) counts the occurrences of the i-th letter in z.
A321840
Number of words w of length n such that each letter of the quaternary alphabet is used at least once and for every prefix z of w we have #(z,a_i) = 0 or #(z,a_i) >= #(z,a_j) for all j>i and #(z,a_i) counts the occurrences of the i-th letter in z.
Terms
- a(0) =24a(1) =60a(2) =210a(3) =609a(4) =1961a(5) =5952a(6) =19255a(7) =60812a(8) =200281a(9) =652011a(10) =2185981a(11) =7283988a(12) =24809651a(13) =84207955a(14) =290756694a(15) =1001820292a(16) =3500030779a(17) =12211804429a(18) =43101225586a(19) =151996648798a(20) =541273095677
External references
- oeis: A321840