a(n) = Sum_{k=1..n} binomial(2*k, k) * sigma(k).

Terms

a(0) =2a(1) =20a(2) =100a(3) =590a(4) =2102a(5) =13190a(6) =40646a(7) =233696a(8) =865756a(9) =4191364a(10) =12656548a(11) =88372916a(12) =233981316a(13) =1196779716a(14) =4919600196a(15) =23553092286a(16) =65558004246a(17) =419488280946