Self-convolution of A120588, such that a(n) = 3*A120588(n) for n >= 2.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =15a(5) =42a(6) =126a(7) =396a(8) =1287a(9) =4290a(10) =14586a(11) =50388a(12) =176358a(13) =624036a(14) =2228700a(15) =8023320a(16) =29084535a(17) =106073010a(18) =388934370a(19) =1432916100a(20) =5301789570a(21) =19692361260a(22) =73398801060a(23) =274447690920