a(n) = G_n(6), where G is the Goodstein function defined in A266201.

Terms

a(0) =6a(1) =29a(2) =257a(3) =3125a(4) =46655a(5) =98039a(6) =187243a(7) =332147a(8) =555551a(9) =885775a(10) =1357259a(11) =2011162a(12) =2895965a(13) =4068068a(14) =5592391a(15) =7542974a(16) =10003577a(17) =13068280a(18) =16842083a(19) =21441506a(20) =26995189a(21) =33644492a(22) =41544095a(23) =50862597a(24) =61783119a(25) =74503901a(26) =89238903a(27) =106218405a(28) =125689607a(29) =147917229