jómfrúrarefnums

Jómfrúrarefnums is an Icelandic term that translates literally to "virgin number". It refers to a prime number that remains prime when all of its digits are successively removed from the left. For example, the number 373 is a jómfrúrarefnums. If we remove the leftmost digit, 3, we are left with 73, which is also a prime number. Removing the leftmost digit of 73, 7, leaves us with 3, which is a prime number. Thus, 373 is a jómfrúrarefnums.

Other examples of jómfrúrarefnums include 2, 3, 5, 7, 23, 37, 53, 73, 373, 733, 3733, and 37337. The concept is a specific case of left-truncatable primes, where the truncation is only allowed from the left. The study of such numbers is a niche area within number theory, often explored by amateur mathematicians and enthusiasts. Determining whether a large number is a jómfrúrarefnums requires checking the primality of the original number and all subsequent numbers formed by removing its leftmost digit. The sequence of jómfrúrarefnums is finite, with the largest known being 37337999.