a(n) = A192815(n)/2.

Terms

a(0) =0a(1) =1a(2) =2a(3) =7a(4) =36a(5) =173a(6) =806a(7) =3763a(8) =17608a(9) =82393a(10) =385482a(11) =1803487a(12) =8437740a(13) =39476613a(14) =184694254a(15) =864105611a(16) =4042781584a(17) =18914450865a(18) =88492648850a(19) =414019362743