From P-positions in a certain game.

Terms

a(0) =0a(1) =2a(2) =6a(3) =11a(4) =20a(5) =38a(6) =71a(7) =136a(8) =265a(9) =523a(10) =1036a(11) =2061a(12) =4110a(13) =8207a(14) =16400a(15) =32785a(16) =65554a(17) =131092a(18) =262165a(19) =524310a(20) =1048599a(21) =2097176a(22) =4194329a(23) =8388634a(24) =16777243a(25) =33554460a(26) =67108893a(27) =134217758a(28) =268435487a(29) =536870944