Number of primitive (aperiodic) reversible strings with n beads using exactly four different colors.

A056320

Number of primitive (aperiodic) reversible strings with n beads using exactly four different colors.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =12a(4) =120a(5) =780a(6) =4212a(7) =20412a(8) =93360a(9) =409260a(10) =1749780a(11) =7338000a(12) =30394560a(13) =124700928a(14) =508291692a(15) =2061586800a(16) =8332140720a(17) =33585682920a(18) =135116412660a(19) =542785390680

External references