Number of Twopins positions.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =2a(7) =2a(8) =3a(9) =3a(10) =4a(11) =5a(12) =6a(13) =8a(14) =9a(15) =12a(16) =14a(17) =18a(18) =22a(19) =27a(20) =34a(21) =41a(22) =52a(23) =63a(24) =79a(25) =97a(26) =120a(27) =149a(28) =183a(29) =228