What does digit sum exactly means?

1- Sum the digits on both numbers and check the result is prime?
2- Sum the digits in each number and check both results are prime?
3- Sum corresponding digits and check all results are prime?
4- Anything else?

2)

oh dear.

I have just gone to quite a high number of primes doing the sum of the 2 numbers.

Time to recode it...

Hi,

You say that the right answer is number 2. Then why 1000099 and 1000121 aren't ok ? I mean they are the first two to be prime number with sums which are primes too : 1+9+9 = 19 (prime) and 1+1+2+1 = 5 (prime)

Thx, Romain

Simply because they are not the first two primes to fulfil the constraints.

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