Central binomial coefficients C(2k,k) repeated.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =6a(5) =6a(6) =20a(7) =20a(8) =70a(9) =70a(10) =252a(11) =252a(12) =924a(13) =924a(14) =3432a(15) =3432a(16) =12870a(17) =12870a(18) =48620a(19) =48620a(20) =184756a(21) =184756a(22) =705432a(23) =705432a(24) =2704156a(25) =2704156a(26) =10400600a(27) =10400600a(28) =40116600a(29) =40116600