a(n) = G_n(7), where G is the Goodstein function defined in A266201.

Terms

a(0) =7a(1) =30a(2) =259a(3) =3127a(4) =46657a(5) =823543a(6) =16777215a(7) =37665879a(8) =77777775a(9) =150051213a(10) =273624711a(11) =475842915a(12) =794655639a(13) =1281445305a(14) =2004318063a(15) =3051893870a(16) =4537630813a(17) =6604718946a(18) =9431578931a(19) =13238000758a(20) =18291957825a(21) =24917131658a(22) =33501182551a(23) =44504801406a(24) =58471578053a(25) =76038721330