a(n) = (7*10^n - 43)/9 for n > 0.

Terms

a(0) =3a(1) =73a(2) =773a(3) =7773a(4) =77773a(5) =777773a(6) =7777773a(7) =77777773a(8) =777777773a(9) =7777777773a(10) =77777777773a(11) =777777777773