Second convolution of A001405 (central binomial numbers).

Terms

a(0) =1a(1) =3a(2) =9a(3) =22a(4) =54a(5) =123a(6) =281a(7) =618a(8) =1362a(9) =2934a(10) =6330a(11) =13452a(12) =28620a(13) =60243a(14) =126921a(15) =265282a(16) =554874a(17) =1153506a(18) =2399390a(19) =4966740a(20) =10286196a(21) =21219038a(22) =43790154a(23) =90076452a(24) =185353204a(25) =380364108a(26) =780786516a(27) =1599015192a(28) =3275589144