Expansion of bracket function.

Terms

a(0) =1a(1) =-6a(2) =21a(3) =-56a(4) =126a(5) =-252a(6) =463a(7) =-804a(8) =1365a(9) =-2366a(10) =4368a(11) =-8736a(12) =18565a(13) =-40410a(14) =87381a(15) =-184604a(16) =379050a(17) =-758100a(18) =1486675a(19) =-2884776a(20) =5592405a(21) =-10919090a(22) =21572460a(23) =-43144920a(24) =87087001a(25) =-176565486a(26) =357913941a(27) =-723002336