The number of n-digit numbers in A270048.

Terms

a(0) =4a(1) =6a(2) =17a(3) =45a(4) =131a(5) =381a(6) =1123a(7) =3334a(8) =9973a(9) =29991a(10) =90601a(11) =274746a(12) =835844a(13) =2549874a(14) =7797469a(15) =23894630a(16) =73358721a(17) =225589420a(18) =694745922a(19) =2142444490a(20) =6614766985a(21) =20445300258a(22) =63256499281a(23) =195890524486a(24) =607136782567