Number of different strings of length n obtained from "abcd" by iteratively duplicating any substring.

A137744

Number of different strings of length n obtained from "abcd" by iteratively duplicating any substring.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =4a(6) =13a(7) =40a(8) =119a(9) =348a(10) =1014a(11) =2966a(12) =8726a(13) =25820a(14) =76823a(15) =229814a(16) =691186a(17) =2089850a(18) =6351448a(19) =19398726a(20) =59525641a(21) =183462778a(22) =567794458a(23) =1764118964a(24) =5501252365a(25) =17214902088a(26) =54047671324a(27) =170218070930a(28) =537678825668

External references