Total path length of the complete ternary tree of height n.

Terms

a(0) =0a(1) =3a(2) =21a(3) =102a(4) =426a(5) =1641a(6) =6015a(7) =21324a(8) =73812a(9) =250959a(10) =841449a(11) =2790066a(12) =9167358a(13) =29893557a(14) =96855123a(15) =312088728a(16) =1000836264a(17) =3196219035a(18) =10169787837a(19) =32252755710a(20) =101988443730a(21) =321655860993