find the missing number; 8 1 4 5 7 # ;81 4 25 36 ?

To find the missing number in the sequence 8, 1, 4, 5, 7, #, 81, 4, 25, 36, ?, we can analyze the pattern and logic behind the given sequence.

Looking at the numbers, we can see that there are alternating squares and additions involved. Let's break down the sequence to better understand it:

8 → 1 (Square - 8 is the square of 2)
1 → 4 (Add 3 - 1 + 3 = 4)
4 → 5 (Add 1 - 4 + 1 = 5)
5 → 7 (Add 2 - 5 + 2 = 7)

From the above pattern, we can observe that the first four numbers in the sequence are obtained by two different operations: squaring and addition. Then, we encounter a missing number represented by the symbol '#', which we are trying to find. Following that, the sequence continues with squared numbers and an additional pattern.

Let's continue analyzing the pattern:

# → 81 (Square - # is the square of 9)
81 → 4 (Add -77 - 81 + (-77) = 4)
4 → 25 (Square - 4 is the square of 2)
25 → 36 (Square - 25 is the square of 5)

Based on the pattern, we can infer that the missing number, which replaces the '#,' is found by squaring 9, resulting in 81. Therefore, the missing number is 81.

Here is the completed sequence: 8, 1, 4, 5, 7, 81, 4, 25, 36, 81.