A120901 Central terms of triangle A120898 (cascadence of 1+2x+x^2).
1, 1, 5, 14, 43, 156, 535, 1956, 7175, 26418, 98375, 367176, 1378022, 5193625, 19641164, 74535167, 283651169, 1082274210, 4139129734, 15863315213, 60913982404, 234317240601, 902804442380, 3483620505111, 13460665855850
Offset: 0