The combination of interval sequence and equal difference equal ratio mixed sequence, such as: 3,1,5,1,11,1,21,1, (43) How to solve it?

The combination of interval sequence and equal difference equal ratio mixed sequence, such as: 3,1,5,1,11,1,21,1, (43) How to solve it?

Divide a sequence into two sequences
3,5,11,21.
1,1,1,1,1.
It is represented by piecewise function