Which of the following numbers will replace the question mark (?) in the given series?
1, 6, 31, 156, ?, 3906

Given,
1, 6, 31, 156, ?, 3906
First, check the difference:
6−1=5
31−6=25
156−31=125
Next difference: ?−156=
3906−?=
So the differences are:
+5, +25, +125, ?
Now observe:
These differences are powers of 5:
5¹ = 5
5²=2
5³=125
Next: 5⁴=625
So,
Next number=156+625= 781

So, 781 will complete the series .

Thus the correct answer is: Option A