a(n) = Sum_{d|n} (n/d)^d * binomial(d+n,n).

Terms

a(0) =2a(1) =12a(2) =32a(3) =150a(4) =282a(5) =1890a(6) =3488a(7) =21582a(8) =54650a(9) =282612a(10) =705564a(11) =4072224a(12) =10400782a(13) =55006530a(14) =158987232a(15) =790611350a(16) =2333606526a(17) =11573213196a(18) =35345264180a(19) =168673694070a(20) =540848064614