通项公式是 An = 9n³-42n²+75n-37
测算 A1 = 9*1-42*1+75*1-37 = 5
A2 = 9*8-42*4+75*2-37 = 17
A3 = 9*27-42*9+75*3-37 = 53
A4 = 9*64-42*16+75*4-37 = 167 测算通过!