a(n) is the least positive number k such that 3^n+k has n prime factors counted with multiplicity.

Terms

a(0) =2a(1) =1a(2) =1a(3) =3a(4) =9a(5) =7a(6) =21a(7) =63a(8) =157a(9) =471a(10) =5a(11) =15a(12) =45a(13) =135a(14) =405a(15) =1215a(16) =3645a(17) =10935a(18) =32805a(19) =98415a(20) =295245a(21) =885735a(22) =2657205a(23) =4409119a(24) =2741597a(25) =8224791a(26) =16285765a(27) =15302863a(28) =45908589a(29) =137725767