Central binomial coefficient - 1.

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =5a(5) =9a(6) =19a(7) =34a(8) =69a(9) =125a(10) =251a(11) =461a(12) =923a(13) =1715a(14) =3431a(15) =6434a(16) =12869a(17) =24309a(18) =48619a(19) =92377a(20) =184755a(21) =352715a(22) =705431a(23) =1352077a(24) =2704155a(25) =5200299a(26) =10400599a(27) =20058299a(28) =40116599a(29) =77558759