Mix A001021, 2*A001021.

Terms

a(0) =1a(1) =2a(2) =12a(3) =24a(4) =144a(5) =288a(6) =1728a(7) =3456a(8) =20736a(9) =41472a(10) =248832a(11) =497664a(12) =2985984a(13) =5971968a(14) =35831808a(15) =71663616a(16) =429981696a(17) =859963392a(18) =5159780352a(19) =10319560704a(20) =61917364224a(21) =123834728448a(22) =743008370688