a(3) = 1, otherwise a(n) = n*2^(n-3) - 2^(n-2) - 2.

Terms

a(0) =1a(1) =2a(2) =10a(3) =30a(4) =78a(5) =190a(6) =446a(7) =1022a(8) =2302a(9) =5118a(10) =11262a(11) =24574a(12) =53246a(13) =114686a(14) =245758a(15) =524286a(16) =1114110a(17) =2359294a(18) =4980734a(19) =10485758a(20) =22020094a(21) =46137342a(22) =96468990a(23) =201326590a(24) =419430398a(25) =872415230a(26) =1811939326a(27) =3758096382a(28) =7784628222a(29) =16106127358