3*Volume of the root-n Waterman polyhedron as defined in A119870.

Terms

a(0) =20a(1) =32a(2) =136a(3) =160a(4) =244a(5) =348a(6) =516a(7) =600a(8) =744a(9) =768a(10) =1016a(11) =1088a(12) =1484a(13) =1484a(14) =1628a(15) =1700a(16) =2092a(17) =2272a(18) =2608a(19) =2680a(20) =2920a(21) =3040a(22) =3136a(23) =3432a(24) =3996a(25) =4092a(26) =4620a(27) =4716a(28) =4788a(29) =4788