7 500 000 Lira Cahit Arf

Cahit Arf, the mathematician this coin honors, developed what is now called the Arf invariant in 1941 — a contribution to algebraic topology that remains embedded in modern K-theory and the mathematics underlying certain cryptographic systems. He published the work while based in Istanbul, having returned from Göttingen where he trained under Helmut Hasse. The Turkish academic establishment claimed him enthusiastically, and his face later appeared on the 10 lira banknote series beginning in 2009.

The denomination — 7,500,000 lira — reflects Turkey's currency in the final throes of its chronic inflation crisis, just two years before the redenomination that stripped six zeros and introduced the New Turkish Lira in 2005.