Central coefficients of a scaled Legendre triangle.

Terms

a(0) =1a(1) =0a(2) =2a(3) =4a(4) =22a(5) =136a(6) =504a(7) =5136a(8) =16966a(9) =240368a(10) =752800a(11) =13660480a(12) =41492284a(13) =918172848a(14) =2734083968a(15) =71399743744a(16) =209681631814