Number of heptagonal numbers with n digits.

Terms

a(0) =3a(1) =4a(2) =14a(3) =43a(4) =137a(5) =432a(6) =1368a(7) =4324a(8) =13676a(9) =43245a(10) =136755a(11) =432455a(12) =1367545a(13) =4324555a(14) =13675445a(15) =43245553a(16) =136754447a(17) =432455532a(18) =1367544468a(19) =4324555320a(20) =13675444680a(21) =43245553203a(22) =136754446797a(23) =432455532033