Mancko wrote:What does the ն word means?
տասնհինգ (15) is տաս ն հինգ (10 ն 5)
Is it 'plus', 'and', or something else?
According to the etymological info in the Wiktionary, տասնհինգ is formed from just տաս
ն (Old Armenian for ‘ten’) + հինգ (‘five’), so that ն by itself means nothing.
Mancko wrote:I don't understand the tens either, say how to build them from the digits?
մեկ -> տաս (1 -> 10)
երկու -> քսան (2 -> 20)
երեք -> երեսուն (3 -> 30)
չորս -> քառասուն (4 -> 40)
հինգ -> հիսուն (5 -> 50)
...
It seems we add -սուն at the end of the digit root, but it's only a guess as I can't tell what the root is.
They apparently need to be learnt as vocabulary, because they seem to descend directly from Proto-Indo-European words and aren’t ‘derivable’, so to speak, from smaller units in the modern language. The -սուն bit, for instance, seems (according to the Wiktionary once again) to come from the PIE word for ‘ten’, which is also the ultimate source of Old Armenian տասն above (besides English ‘ten’, Portuguese ‘dez’ etc.).
Mancko wrote:Also, can someone write down some random numbers, like
256
2,567
7,543,896
How curious that none of my materials seem to explain number formation…

Apparently you just give the numbers one after another, spelling them as a single word up to 100, and as separate words from 101 on. Based on that, I
think those’d be:
256 = երկու հարյուր հիսունվեց
2,567 = երկու հազար հինգ հարյուր վաթսունյոթ
7,543,896 = յոթ միլիոն հինգ հարյուր քառասուներեք հազար ութ հարյուր իննսունվեց
Worth pointing out that Armenia seems to use a decimal comma, which means they use either a dot or a (thin) space when grouping digits (that is, 2.567, 7.543.896 etc.).