Sam Benry

Ranch Hand

Posts: 89

posted 9 years ago

I have this question from euler

I can't figure out the eleven prime numbers, why are these prime numbers wrong:

11

13

17

23

31

37

53

71

73

113

131

aren't they all truncatable from both left and right? and if they are, there are still many more truncatable prime numbers from both left and right... what am I doing wrong?

The number 3797 has an interesting property. Being prime itself, it is possible to continuously remove digits from left to right, and remain prime at each stage: 3797, 797, 97, and 7. Similarly we can work from right to left: 3797, 379, 37, and 3.

Find the sum of the only eleven primes that are both truncatable from left to right and right to left.

NOTE: 2, 3, 5, and 7 are not considered to be truncatable primes.

I can't figure out the eleven prime numbers, why are these prime numbers wrong:

11

13

17

23

31

37

53

71

73

113

131

aren't they all truncatable from both left and right? and if they are, there are still many more truncatable prime numbers from both left and right... what am I doing wrong?