For what it's worth, here's a short script in python that will do this POW:
while(h is None or h[-6:]!='abcdef'):
print('SHA256(' + hex(p) + ')=' + h)
This took about 15 seconds to run on my (decent, fairly new)...
This is not possible using hashcat, unless you're ready to change the source code to suit your needs.
For example, you can adapt s3inlc's fork which added an option to check for hashes with some specific properties (starting / ending with as much 0 as possible, etc.).
Someone else may correct me, but I don't believe there is any way to answer that query except by brute force (which is, of course, the point). A strong hashing algorithm returns effectively random output for even small changes in the input, so they are specifically designed so that you can't do exactly what you are trying to do. If you were able to guess ...