From solution to a counting problem.

Terms

a(0) =0a(1) =24a(2) =120a(3) =360a(4) =824a(5) =1664a(6) =2992a(7) =5000a(8) =7848a(9) =11808a(10) =17024a(11) =23888a(12) =32576a(13) =43432a(14) =56816a(15) =73136a(16) =92616a(17) =115872a(18) =143104a(19) =174928a(20) =211808a(21) =254312a(22) =302680a(23) =357832a(24) =420136a(25) =490232a(26) =568664a(27) =656360a(28) =753496a(29) =861376