RSA 3072 is 65,536 more difficult to factor than 2048? If RSA 3072 is equal to 128 bit symmetric and 2048 is equal to 112 bit symmetric then 128-112= 16 and 2^16= 65,536. In that case wouldn't this make 3072 more future proof against quantum computers or does Shor's algorithm mean they will both be equally useless?

Also, how many bits of symmetric is RSA 4096 equal to?
If RSA 3072 is equal to 128 bit symmetric and 2048 is equal to 112 bit symmetric...


To be precise, a 2048 bit composite is estimated to take approximately $2^{112}$ operations using the Number Field Sieve algorithm; 3072 bit composites are estimated to take approximately $2^{128}$ operations using that same operation.

Since the Number Field Sieve (NFS) algorithm is the fastest factoring algorithm known on a classical computer for large general composites, this is taken as the work estimate


  In that case wouldn't this make 3072 more future proof against quantum computers or does Shor's algorithm mean they will both be equally useless?


Once we bring Quantum Computers and Shor's algorithm into the mix, that opens up another algorithm that is potentially more efficient than NFS.  And, for Shor's, 3072 bit integers isn't that much more difficult that 2048 bit ones.