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A permutable prime, also known as anagrammatic prime, is a prime number which, in a given base, can have its digits' positions switched through any permutation and still be a prime number. H. E. Richert, who is supposedly the first to study these primes, called them permutable primes, but later they were also called absolute primes.
In base 10, all the permutable primes with fewer than 49,081 digits are known
Of the above, there are 16 unique permutation sets, with smallest elements
Note Rn = 10 n − 1 9 {\displaystyle {\tfrac {10^{n}-1}{9}}} is a repunit, a number consisting only of n ones. Any repunit prime is a permutable prime with the above definition, but some definitions require at least two distinct digits.