My AI startup tried ‘nerd-sniping’ by posting math puzzles with a hidden message all over San Francisco. It worked.

This as-told-to essay is based on a conversation with Felicia Tang, chief of staff at startup Exa. It has been edited for length and clarity.

San Francisco is a super competitive job market, especially for machine learning engineers and high-quality backend and full-stack engineers.

For us, outbound hiring usually means our cofounders tapping into their Harvard networks, or us identifying companies we think have good engineers and manually sending personalized…