Number of permutations of [n] whose compositional square is the identity permutation or its reverse.

A383835

Number of permutations of [n] whose compositional square is the identity permutation or its reverse.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =4a(4) =12a(5) =28a(6) =76a(7) =232a(8) =776a(9) =2632a(10) =9496a(11) =35696a(12) =140272a(13) =568624a(14) =2390480a(15) =10349536a(16) =46208416a(17) =211800992a(18) =997313824a(19) =4809701440a(20) =23758694336a(21) =119952723136a(22) =618884638912

External references