The sequence c[n] defined in A126940.

Terms

a(0) =0a(1) =2a(2) =4a(3) =12a(4) =42a(5) =132a(6) =414a(7) =1320a(8) =4198a(9) =13322a(10) =42308a(11) =134392a(12) =426832a(13) =1355612a(14) =4305518a(15) =13674594a(16) =43431194a(17) =137939776a(18) =438104256a(19) =1391442706a(20) =4419296770a(21) =14035924512a(22) =44578852058a(23) =141584833642a(24) =449681053086