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

Terms

a(0) =5a(1) =41a(2) =293a(3) =2057a(4) =14405a(5) =100841a(6) =705893a(7) =4941257a(8) =34588805a(9) =242121641a(10) =1694851493a(11) =11863960457a(12) =83047723205a(13) =581334062441