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

Terms

a(0) =2a(1) =22a(2) =131a(3) =806a(4) =3607a(5) =20395a(6) =84254a(7) =422230a(8) =1842359a(9) =8616007a(10) =33843614a(11) =173724659a(12) =676938316a(13) =2983855666a(14) =12806013721a(15) =57981927158a(16) =223432922515