a(n) = 7^n - 6^n + 1.

Terms

a(0) =1a(1) =2a(2) =14a(3) =128a(4) =1106a(5) =9032a(6) =70994a(7) =543608a(8) =4085186a(9) =30275912a(10) =222009074a(11) =1614529688a(12) =11664504866a(13) =83828316392a(14) =599858908754