Number of stacks of n triangles, pointing upwards or downwards depending on row parity.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =7a(6) =13a(7) =24a(8) =45a(9) =84a(10) =156a(11) =291a(12) =543a(13) =1013a(14) =1889a(15) =3524a(16) =6575a(17) =12266a(18) =22883a(19) =42691a(20) =79647a(21) =148593a(22) =277221a(23) =517197a(24) =964911a(25) =1800189a(26) =3358526a(27) =6265846a(28) =11689902a(29) =21809313