# Complete the series:

$$4427, 827, 67, 31, 9, ?$$

Choose between:

• (a): $$7$$
• (b): $$6$$
• (c): $$5$$
• (d): $$4$$

Looking at the numbers I think that there must be some exponential relationship but couldn't find it. I took the sequence of differences between the numbers which is $$3600, 760, 36, 22, ?$$
But I still couldn't find any relationship.

I do not think the question is wrong.

Source : NTSE Test Series, MAT

4427 = 672 - 2 × 31
31 =  72 - 2 ×  9