Convert a number to sha-1
There is no why it is identical. The input form of the data does not influence what the output of a secure hash function should look like. The input of a hash should be unrelated to the output except for the mapping performed in the hash function itself. There should be no method of calculating the output other than to execute the hash function.

The best way to find another hash with the same property is to brute force it; go through a lot of numbers, convert them to bytes, calculate the hash and compare against the hexadecimal representation of the output. As each hexadecimal digit represents 4 bits, you would have to perform $2^{44}$ calculations (as I don't see how the birthday paradox would help you here). Note that, as CodesInChaos mentioned in a comment, that rainbow tables could speed up searches for cases where the input has properties that are reflected in the output.

If you get the wrong hash output, then it is likely that your conversion from the given number to bytes is failing. You may want to try another encoding.