Even 21 was only possible by cheating (optimizing away the difficult part using prior knowledge of the results) [1]. Craig Gidney has a blog post that shows the actual quantum circuit for factoring 21 which is far beyond the capabilities of current quantum computers [2].
Overview of QC factoring records, applied sleight-of-hand tricks, and their replication using a VIC-20 8-bit home computer from 1981, an abacus, and a dog:
Even 21 was only possible by cheating (optimizing away the difficult part using prior knowledge of the results) [1]. Craig Gidney has a blog post that shows the actual quantum circuit for factoring 21 which is far beyond the capabilities of current quantum computers [2].
[1] https://www.nature.com/articles/nature12290
[2] https://algassert.com/post/2500
And it was done in 2012. I admit I’m surprised there hasn’t been more progress since.
Overview of QC factoring records, applied sleight-of-hand tricks, and their replication using a VIC-20 8-bit home computer from 1981, an abacus, and a dog:
https://eprint.iacr.org/2025/1237.pdf