Number of quaternary steady words of length n (with respect to the permutations of symbols).

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =5a(5) =7a(6) =9a(7) =12a(8) =16a(9) =21a(10) =28a(11) =37a(12) =45a(13) =58a(14) =73a(15) =93a(16) =101a(17) =124a(18) =150a(19) =179a(20) =216a(21) =257a(22) =309a(23) =376a(24) =453a(25) =551a(26) =662a(27) =798a(28) =957a(29) =1149