BULGARIA: 20 Leva (1989) in silver (0,500) commemorating the Academy of Science. National arms within pegged circle on obverse. Academy building, two dates above, denomination and date below within pegged circle on reverse. Inside slab by NGC "PF 67 ULTRA CAMEO / ACADEMY OF SCIENCE ANNIV.". Cert number: 6389132-102. (KM 183) & (Nikolov 235).