Number of Twopins positions.

Terms

a(0) =1a(1) =2a(2) =4a(3) =6a(4) =9a(5) =12a(6) =18a(7) =26a(8) =41a(9) =62a(10) =96a(11) =142a(12) =212a(13) =308a(14) =454a(15) =662a(16) =979a(17) =1438a(18) =2128a(19) =3126a(20) =4606a(21) =6748a(22) =9910a(23) =14510a(24) =21298a(25) =31212a(26) =45820a(27) =67176a(28) =98571a(29) =144476