how to replace formatNumber standard function with udf?

Hi Expert,

Currently I am using formatNumber standard function to create 18 digits number, but its failing when alpha numeric comes as input. now Can you please some udf to handle alphanumeric input and required to 18 digits output. if input length less than 18 digits, then zeros should be padded. Please suggest if it is possible thru graphical.

Please provide the udf earliest. thanks in advance.

Thanks,

chandar