The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
D-finite with recurrence: n*a(n) + (-7*n+5)*a(n-1) + 3*(5*n-8)*a(n-2) + (-13*n+33)*a(n-3) + 2*(2*n-7)*a(n-4) = 0. - R. J. Mathar, Jan 28 2020
EXAMPLE
a(3)=17 since can map (1,2,3) to (1,1,1), (1,1,2), (1,1,3), (1,2,2), (1,2,3), (1,3,3), (2,1,1), (2,2,1), (2,2,2), (2,2,3), (2,3,3), (3,1,1), (3,2,1), (3,2,2), (3,3,1), (3,3,2), or (3,3,3) but not for example to (1,3,2).