Card-matching numbers (Dinner-Diner matching numbers).

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =120a(7) =14400a(8) =0a(9) =360000a(10) =0a(11) =1440000a(12) =0a(13) =1440000a(14) =0a(15) =360000a(16) =0a(17) =14400a(18) =3891456000a(19) =26179200000a(20) =83980800000a(21) =171676800000a(22) =249091200000a(23) =270869184000a(24) =226368000000a(25) =150465600000a(26) =77760000000