Finding cb numbers

#1

can u give me a hint on how to do this question

#2

also explain me with one example like 2934191, will it consider each character or it may not count each and every character to get the maximum number of results?

#3

One thing students miss in this questions is that they think numbers divisible by primes numbers are not CB numbers. But that is only the case with prime number till and including 29. Numbers divisible by prime number after 29 will also be considered CB numbers. For eg, 31*31 is a CB number, even though it is divisible by 31, but it is not divisible by any number mentioned in line 2 of the question.
Hope this helps.

#4

i got that logic but how to do this question

#5

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