Number of ordered pairs of involutions on [n] that commute.

A362819

Number of ordered pairs of involutions on [n] that commute.

Terms

    a(0) =1a(1) =1a(2) =4a(3) =10a(4) =52a(5) =196a(6) =1216a(7) =5944a(8) =42400a(9) =250912a(10) =2008576a(11) =13815616a(12) =122074624a(13) =950640640a(14) =9158267392a(15) =79258479616a(16) =824644235776

External references