This question presents an interesting pattern.
The rule/pattern to be followed here is:
Left side of the number looking at the previous one: (First digit x Third digit + 1)
Right side: (Second digit x Fourth digit -1)
For example, let us take 6447. Let us look at it's previous number, 9876.
Now,
and
![8* 6-1=47](https://img.qammunity.org/2019/formulas/mathematics/middle-school/qjm1nrjl0w1r321c2ull3ik7djl9jioqwe.png)
that is how we got 6447
Again, for the third number, 2527, let us look at it's previous number, 6447
Now,
![6* 4+1=25](https://img.qammunity.org/2019/formulas/mathematics/middle-school/s63x4wpjixv0fmw36r6dfh8orytn0nzzfh.png)
and
![4* 7-1=27](https://img.qammunity.org/2019/formulas/mathematics/middle-school/bvdot9cq3h9gyuo5tk78e0j1tcjk8hact7.png)
that is how we got 2527
Going by the same logic, the missing number should be 534.
This we got by applying the rule of the pattern as:
![(2* 2)+1=5](https://img.qammunity.org/2019/formulas/mathematics/middle-school/zn665sm6pdi76h2dyhgzg0wiw3j8vkk07u.png)
and
![(5* 7)-1=34](https://img.qammunity.org/2019/formulas/mathematics/middle-school/j3qqp61kp837dvbn797mfftjsneh7igg0f.png)
Thus, we got 534.