Constant term in the expansion of (Sum_{k=0..n} k*(x^k + x^(-k)))^4.

Terms

a(0) =0a(1) =6a(2) =198a(3) =2076a(4) =12060a(5) =49170a(6) =158418a(7) =431544a(8) =1036728a(9) =2258910a(10) =4552350a(11) =8607060a(12) =15430740a(13) =26447850a(14) =43617450a(15) =69571440a(16) =107774832a(17) =162709686a(18) =240084342a(19) =347069580a(20) =492563340a(21) =687485634a(22) =945105282a(23) =1281400104a(24) =1715452200a(25) =2269879950a(26) =2971308366