An oban number is a positive integer whose standard English name does not contain the letter "o" (i.e., "o" is banned), by analogy with the eban numbers. The naming convention omits "and," as described under number. Special names sometimes assigned to a few large numbers are excluded.
The first few are 3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, 19, 20, 23, 25, 26, ... (OEIS A008521).
Under this convention, every integer at least 1000 has a name containing either "thousand" or the suffix "-illion", so there are finitely many oban numbers. In fact, there are a total of 454 of them, the largest of which is 999.
A plot of the oban numbers represented as a sequence of bits is shown above.
