Number of digits in n-th Fermat number (A000215).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =10a(6) =20a(7) =39a(8) =78a(9) =155a(10) =309a(11) =617a(12) =1234a(13) =2467a(14) =4933a(15) =9865a(16) =19729a(17) =39457a(18) =78914a(19) =157827a(20) =315653a(21) =631306a(22) =1262612a(23) =2525223a(24) =5050446a(25) =10100891a(26) =20201782a(27) =40403563a(28) =80807125a(29) =161614249