Number of n-tuples of 4 elements excluding reverse duplicates and those consisting of repetitions of the same element only.

A321579

Number of n-tuples of 4 elements excluding reverse duplicates and those consisting of repetitions of the same element only.

Terms

    a(0) =0a(1) =0a(2) =6a(3) =36a(4) =132a(5) =540a(6) =2076a(7) =8316a(8) =32892a(9) =131580a(10) =524796a(11) =2099196a(12) =8390652a(13) =33562620a(14) =134225916a(15) =536903676a(16) =2147516412a(17) =8590065660a(18) =34359869436a(19) =137439477756a(20) =549756338172

External references