Self-convolution of A138020.

Terms

a(0) =1a(1) =4a(2) =16a(3) =72a(4) =352a(5) =1816a(6) =9728a(7) =53584a(8) =301568a(9) =1726488a(10) =10022912a(11) =58864240a(12) =349102080a(13) =2087772784a(14) =12576358400a(15) =76237953440a(16) =464736354304