Self-convolution of A004148 (the RNA secondary structure numbers) with itself.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =13a(5) =28a(6) =62a(7) =140a(8) =320a(9) =740a(10) =1728a(11) =4068a(12) =9645a(13) =23010a(14) =55195a(15) =133042a(16) =322078a(17) =782758a(18) =1909091a(19) =4671098a(20) =11462607a(21) =28204212a(22) =69569278a(23) =171993316a(24) =426111203a(25) =1057757858a(26) =2630527679a(27) =6552998126a(28) =16350465147a(29) =40857321696