сӣ

сӣ: thirty

Сӣ раками ҷуфт аст.
Thirty is an even number.
Дарахти чормағз баъди сӣ сол меваи хуб медиҳад.
A walnut tree gives good fruit (produce) after thirty years.

Bonus:
In Tajik, the noun following a number does not take the plural ending (ҳо, он).

сиюм: thirtieth

When a suffix is attached to a word ending in ӣ it is changed to и. Example –
яксаду сию панҷ: one hundred and thirty five

рақам

рақам: number

Чор рақами ҷуфт аст.
Four is an even number.
Рақами ҳавлии мо бисту шаш аст.
Our house number is twenty-six.

Bonus:
Synonyms: адад, шумора

рақам мондан: to number
рақами телефон: phone number
рақами ҷуфт: even number
рақами тоқ: odd number

The word рақам can also mean something that has been written.
рақам кардан: to write

бист

бист: twenty

Рақами хонаи мо бист аст.
Our house number is twenty.
Дар соати бист дақиқа кам нӯҳ аз хона мебароям.
At twenty minutes to nine I leave the house.

Bonus:
When combining thousands, hundreds, tens and digits you use у (or ю), and.
бисту як: twenty-one
саду бист: one hundred and twenty
дусаду бисту панҷ: two hundred and twenty-five

To change a cardinal number to an ordinal number add the suffix ум (or юм).
бистум: twentieth

When writing ordinal numbers often the number is written instead of the word, and then hyphenated with the ending, for example:
20-уми май: 20th of May

When a noun comes after a number, the noun does not take the plural ending.
гулҳо: flowers
бист гул: twenty flowers