How to specify a 16-byte serial number when OpenSSL issues a certificate

How do I specify a 16-byte serial number when OpenSSL issues a certificate?
There was a point in signing the certificate using the OpenSSL function, the project explicitly requires specifying a 16-byte certificate sequence number, such as 0x4c530000000000000100020004000009, where the last 3 bytes are dynamically changing, using OPENSSL_CSR The _sign function is having trouble.

Resource Openssl_csr_sign (mixed $CSR, mixed $cacert, mixed $priv _key, int $days [, array $configargs [, int $serial =0 ]] )

The last parameter can specify the serial number, but the normal int cannot support such a large integer, tried to use sprintf ('%s ', $n), attempted to pass the text directly, either write it in one byte or 0

Which direction should I start to find a solution?

Can have sample code better

Thank you!

------Solution--------------------
Description:
------------
The Certificat defintion OpenSSL allows for numerical serial numbers
Positions or more.
In PHP there are build in integer rerstriction only allowing half the serial
Numbers. Higher numbers has a cleared part ....

The serial needs to being numerical no problem but it need not being an integer
or limited by (allow higher numbers)
------Solution--------------------
The Certificat defintion OpenSSL allows for numerical serial numbers
Positions or more.
In PHP there are build in integer rerstriction only allowing half the serial
Numbers. Higher numbers has a cleared part ....


It seems to mean that the default OpenSSL supports 20-bit-length integers, but PHP's built-in int type is only half the length and the high half is zeroed.

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