Number of perfect rulers with length n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =4a(6) =2a(7) =12a(8) =8a(9) =4a(10) =38a(11) =30a(12) =14a(13) =6a(14) =130a(15) =80a(16) =32a(17) =12a(18) =500a(19) =326a(20) =150a(21) =66a(22) =18a(23) =4a(24) =944a(25) =460a(26) =166a(27) =56a(28) =12a(29) =6