a(n) = sum_of_digits(a(n-1)^a(n-2)) where a(1)=1 and a(2)=2.

Terms

a(0) =1a(1) =2a(2) =2a(3) =4a(4) =7a(5) =7a(6) =25a(7) =34a(8) =151a(9) =331a(10) =1690a(11) =3265a(12) =26449a(13) =64528a(14) =574513a(15) =1671208a(16) =16090657a(17) =54199564a(18) =559922497a(19) =2133503863a(20) =23506132363