Even elements in Pascal's triangle.

Terms

a(0) =2a(1) =4a(2) =6a(3) =4a(4) =10a(5) =10a(6) =6a(7) =20a(8) =6a(9) =8a(10) =28a(11) =56a(12) =70a(13) =56a(14) =28a(15) =8a(16) =36a(17) =84a(18) =126a(19) =126a(20) =84a(21) =36a(22) =10a(23) =120a(24) =210a(25) =252a(26) =210a(27) =120a(28) =10a(29) =330