a(1) = 2; a(n) = a(n-1)-th even nontotient number.

Terms

a(0) =2a(1) =26a(2) =182a(3) =878a(4) =3626a(5) =13508a(6) =46922a(7) =155156a(8) =494468a(9) =1529590a(10) =4615074a(11) =13633310a(12) =39548078a(13) =112918434a(14) =317920082a(15) =883996002