Which case is correct on the numerical specification after بِأَحَدَ عَشَرَ?

Al-Murakkabāt — Compound Numerals, the Twelve Exception and Declining Baalbek

• Accusative numerical tamyīz with fatḥah
• Genitive with kasrah because of bi-
• Nominative with ḍammah
• Indeclinable with no syntactic position