Central coefficient of the triangle A097609.

Terms

a(0) =1a(1) =0a(2) =3a(3) =4a(4) =25a(5) =66a(6) =287a(7) =960a(8) =3789a(9) =13810a(10) =53240a(11) =200652a(12) =771641a(13) =2952054a(14) =11386065a(15) =43910288a(16) =170007429a(17) =658979586a(18) =2560258550a(19) =9960335060a(20) =38811668868a(21) =151418146704a(22) =591464244882