Number of compositions of 2n where the difference between largest and smallest parts equals n.

Terms

a(0) =0a(1) =2a(2) =3a(3) =12a(4) =23a(5) =61a(6) =135a(7) =306a(8) =679a(9) =1499a(10) =3257a(11) =7053a(12) =15167a(13) =32443a(14) =69080a(15) =146533a(16) =309743a(17) =652762a(18) =1371897a(19) =2876284a(20) =6017100a(21) =12562511a(22) =26180328a(23) =54469099a(24) =113151406a(25) =234723068a(26) =486276265a(27) =1006195365a(28) =2079647131a(29) =4293758081