Convolution square of A000219.

Terms

a(0) =1a(1) =2a(2) =7a(3) =18a(4) =47a(5) =110a(6) =258a(7) =568a(8) =1237a(9) =2600a(10) =5380a(11) =10870a(12) =21652a(13) =42350a(14) =81778a(15) =155676a(16) =292964a(17) =544846a(18) =1003078a(19) =1828128a(20) =3301952a(21) =5911740a(22) =10499385a(23) =18502582a(24) =32371011a(25) =56240816a(26) =97073055a(27) =166497412a(28) =283870383a(29) =481212656