Number of involutions of [n] having exactly one peak.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =6a(5) =18a(6) =44a(7) =91a(8) =172a(9) =300a(10) =496a(11) =781a(12) =1186a(13) =1742a(14) =2492a(15) =3479a(16) =4760a(17) =6392a(18) =8448a(19) =11001a(20) =14142a(21) =17962a(22) =22572a(23) =28083a(24) =34628a(25) =42340a(26) =51376a(27) =61893a(28) =74074a(29) =88102