Find out the missing term of the number series given below.

25, ?, 256, 476, 745, 1050

The correct answer is 100.

To find the missing term in the number series, let us analyze the differences between consecutive terms in the series: 25, ?, 256, 476, 745, 1050.

First, we calculate the differences between the known consecutive terms at the end of the series:
$1050-745=305$
$745-476=269$
$476-256=220$

Now, let us examine the differences of these differences (the second level of differences):
$305-269=36=6^2$
$269-220=49=7^2$

We can observe a clear pattern where the second-level differences are consecutive perfect squares in decreasing order ($7^2$, $6^2$, ...). Continuing this pattern backward, the preceding second-level differences must be:
$8^2=64$
$9^2=81$

Using these values, we can determine the first-level differences for the beginning of the series:
Let the difference between 256 and the missing term (?) be $d_2$:
$220-d_2=64\Rightarrow d_2=220-64=156$

Let the difference between the missing term (?) and 25 be $d_1$:
$156-d_1=81\Rightarrow d_1=156-81=75$

Now, we can find the missing term by adding $d_1$ to the first term:
$\text{Missing Term}=25+75=100$

We can verify this result with the next term:
$100+156=256$, which perfectly matches the third term in the series.