Indogermanic forms of the decades 20-90 were based on the unit number (1-9) plus a variant (d)komt- of the word for "10" (*dekmt):

Early Developments: Indogermanic to Proto-Germanic ("*" alone means "was lost")

Later Developments: Proto-Germanic to Gothic, Old English and Old Norse

(Note: The Proto-Germanic plural of *tehun "10" is *tigus "10s.")

20 through 60:

70 through 90 with different pattern-levelings:

100:

1000:

Note: In the Germanic numeric vocabulary, there are three separate numbering systems:

1. The dominant one is, as in all Indogermanic languages, the decimal system, based on 10.
2. In addition, the Babylonian-Assyrian duodecimal system, based on 12, 60 and 120, appears in the pattern changes following the terms for "12" and "60," and in the absence of a simple word for the decimal "100." This resulted from the long contact of the Goths with the neighboring Sassanid Persians in the early centuries of our era (very roughly, 150-375 C.E.).
3. Finally, the old "dual" form of the numeral for "8" (Gothic "ahtau"), as well as the etymology of this word (the Proto-Indogermanic root "*ok-" means "point, tip") indicates an apparently very primitive method of counting on one's fingertips (without the thumb).

The key concept in the development of modern arithmetic and mathematics was the concept of zero. The philosophical preparation for the concept of zero was laid in the Middle Ages by the Christian schoolmen who, following Aristotle, viewed the world as being composed of “form” (forma) without “substance” (materia).  During the crusades, the Latin West borrowed not only Greek philosophy from the Mohammedans (who had translated it into Arabic), but also the Sanskrit numbering system.  That is, the numerals we currently use came from the "Indo-" part of the Indogermanic-speaking peoples.  For the Muslims had conquered northern India and adopted the mathematics originally invented and used there, whence they took these numerals to the west.  Europeans came in contact with them during the crusades.  As a result, the “Arabic” numerals 0 1 2 3 4 5 6 7 8 9 are in actual fact not Arabic at all, but Sanskrit and Indic.  Europeans then took this Arabic-overlayed Sanskritic mathematics (“algebra,” “zero” and “algorithm,” like “alchemy” and “chemistry,” are Arabic words) and, combining it with Graeco-Roman philosophy which viewed the universe as essentially rational, began to develop mathematics as we know it in the West today - a mathematics which is the foundation of science.  “Zero” (same word as “cipher”) was viewed as pure “form” without substance, whereas the other digits were thought of as various levels of form with substance.  This made modern calculations possible (Imagine having to multiply and divide with Roman numerals!).  Our history, thus, is a history of the synthesis of ideas.  We take the best ideas from any and every source and combine them with the best ideas from elsewhere, thereby creating new intellectual structures much more powerful than any of its components.  No other branch of man has come anywhere close to us in this respect.