Earlier quoted context omitted.
Russian numbers are ten based and rather straightforward; odin dva tri ... desyat (10) odinnadtsat dvenadtsat trinadtsat ... dvadtsat (20) there is no irregularity other than 40 which is sorok instead of chetiredesyat
Foreign learners do not generally find Russian numbers to be "straightforward". Not only do nouns qualified by numbers take different numerative cases (the genitive singular for 2–4, the genitive plural for 5–10), but the declension of compound numerals is also surprising for speakers of many languages. Compound hundreds are also unpredictable. Yes, historically the varying forms are clear (the back yer in Common Sla…
For me Russian numbers were simpler than French because you could learn the basic idea quickly, and then pick up subtle sound shifts by watching tv/reading.
(disclaimer, i am not a native speaker but learned Russian at school age so may be misgudging the difficulty of the language)