A hierarchical sequence (S(W'2{3}*c) - see A059126).

Terms

a(0) =12a(1) =48a(2) =144a(3) =384a(4) =960a(5) =2304a(6) =5376a(7) =12288a(8) =27648a(9) =61440a(10) =135168a(11) =294912a(12) =638976a(13) =1376256a(14) =2949120a(15) =6291456a(16) =13369344a(17) =28311552a(18) =59768832a(19) =125829120a(20) =264241152a(21) =553648128a(22) =1157627904a(23) =2415919104a(24) =5033164800a(25) =10468982784a(26) =21743271936a(27) =45097156608a(28) =93415538688