Define an emirpimes ("semiprime" spelled backwards) as a semiprime whose (base 10) reversal is a different semiprime. The first such number is 15, because 15 reversed is 51 and both 15 and 51 are semiprimes (i.e., 15 = 3×5 and 51 = 3×17). A list of the first emirpimeses (or "semirpimes") are 15, 26, 39, 49, 51, 58, 62, 85, 93, 94, 115, 122, 123, ... (OEIS A097393). A binary plot of the semirpimes is illustrated above. The numbers of semirpimes less than 10^n for n = 1, 2, ... are 0, 10, 90, 898, 7200, 60732, ... (OEIS A097394).

emirp | palindromic prime | reversal | semiprime