Number of square involutions of n.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =22a(5) =52a(6) =114a(7) =260a(8) =564a(9) =1256a(10) =2698a(11) =5908a(12) =12588a(13) =27224a(14) =57620a(15) =123432a(16) =259816a(17) =552400a(18) =1157466a(19) =2446004a(20) =5105532a(21) =10735352a(22) =22334524a(23) =46766200a(24) =97021272a(25) =202431152a(26) =418935364a(27) =871425160a(28) =1799558584