Number of ferrites M_4Y_n that repeat after 6n+20 layers.

Terms

a(0) =0a(1) =1a(2) =2a(3) =2a(4) =3a(5) =6a(6) =6a(7) =9a(8) =13a(9) =15a(10) =18a(11) =25a(12) =27a(13) =34a(14) =42a(15) =47a(16) =54a(17) =67a(18) =72a(19) =84