a(n) = n!/3 - 1.

A139173

a(n) = n!/3 - 1.

Terms

    a(0) =1a(1) =7a(2) =39a(3) =239a(4) =1679a(5) =13439a(6) =120959a(7) =1209599a(8) =13305599a(9) =159667199a(10) =2075673599a(11) =29059430399a(12) =435891455999

External references