Harmonic-geometric numbers.

Terms

a(0) =0a(1) =1a(2) =4a(3) =21a(4) =138a(5) =1095a(6) =10208a(7) =109473a(8) =1328470a(9) =18003675a(10) =269580492a(11) =4420677525a(12) =78801184322