a(n) = A027170(2n-1, n-1).

Terms

a(0) =3a(1) =19a(2) =76a(3) =283a(4) =1046a(5) =3890a(6) =14582a(7) =55051a(8) =209062a(9) =797806a(10) =3056868a(11) =11752674a(12) =45316896a(13) =175175816a(14) =678639146a(15) =2634146411a(16) =10241938406a(17) =39882831446a(18) =155519160716a(19) =607181138846