Self-convolution of A013999.

Terms

a(0) =1a(1) =2a(2) =5a(3) =20a(4) =104a(5) =632a(6) =4396a(7) =34680a(8) =307236a(9) =3026472a(10) =32849364a(11) =389704800a(12) =5017492320a(13) =69678231552