Number of pentagonal numbers with n digits.

Terms

a(0) =3a(1) =6a(2) =17a(3) =56a(4) =177a(5) =558a(6) =1766a(7) =5583a(8) =17655a(9) =55829a(10) =176550a(11) =558297a(12) =1765493a(13) =5582976a(14) =17654924a(15) =55829769a(16) =176549231a(17) =558297692a(18) =1765492316a(19) =5582976912a(20) =17654923165a(21) =55829769118a(22) =176549231655a(23) =558297691180