CiteSeer
Trigger: !citeseer
Try it
Kagi would openhttps://citeseer.ist.psu.edu/search?q=riemann+hypothesis&submit=Search&sort=rlv&t=doc
Run @citeseer in Kagi for Kagi's own results from citeseer.ist.psu.edu only
URL pattern: https://citeseer.ist.psu.edu/search?q=query&submit=Search&sort=rlv&t=doc
Searches citeseer.ist.psu.edu, filed under Academic (math/cs).