Partial sums of the central trinomial coefficients (A002426).

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =31a(5) =82a(6) =223a(7) =616a(8) =1723a(9) =4862a(10) =13815a(11) =39468a(12) =113257a(13) =326198a(14) =942425a(15) =2730032a(16) =7926659a(17) =23061590a(18) =67214399a(19) =196211252a(20) =573590621a(21) =1678941350a(22) =4920076877a(23) =14433305000a(24) =42381641381a(25) =124558477682a(26) =366371703833