a(n) = 7*n! - 1.

Terms

a(0) =6a(1) =6a(2) =13a(3) =41a(4) =167a(5) =839a(6) =5039a(7) =35279a(8) =282239a(9) =2540159a(10) =25401599a(11) =279417599a(12) =3353011199a(13) =43589145599a(14) =610248038399