Partial sums of floor(3^n/4).

Terms

a(0) =0a(1) =2a(2) =8a(3) =28a(4) =88a(5) =270a(6) =816a(7) =2456a(8) =7376a(9) =22138a(10) =66424a(11) =199284a(12) =597864a(13) =1793606a(14) =5380832a(15) =16142512a(16) =48427552a(17) =145282674a(18) =435848040a(19) =1307544140a(20) =3922632440a(21) =11767897342a(22) =35303692048a(23) =105911076168a(24) =317733228528