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In written English, we always tend to write the number out as a word, twenty, especially if we want to be more formal.
With larger numbers, it is best to write the number out in digits, so "129,650" is likely to be written as numbers. Sometimes with large numbers with lots of zeros, it is easier to write the word rather than the figures: so 100,000,000 becomes a hundred million.
Figures should be used:
(i) for numbers over nine;
(ii) when the material contains a sequence of stated quantities, numbers, ages, etc (example: children in the 7–12 age group);
(iii) for numbers of sections, clauses, paragraphs etc; and
(iv) wherever words would appear clumsy.
Written numbers 
Linear Mode
