a(n) = 4^n - C(4,3)*3^n + C(4,2)*2^n - C(4,1).
A000919
a(n) = 4^n - C(4,3)*3^n + C(4,2)*2^n - C(4,1).
Terms
- a(0) =0a(1) =0a(2) =0a(3) =24a(4) =240a(5) =1560a(6) =8400a(7) =40824a(8) =186480a(9) =818520a(10) =3498000a(11) =14676024a(12) =60780720a(13) =249401880a(14) =1016542800a(15) =4123173624a(16) =16664094960a(17) =67171367640a(18) =270232006800
External references
- oeis: A000919