Binary plot of the semirpimes

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).

See also

Emirp, Palindromic Prime, Reversal, Semiprime

This entry contributed by Jonathan Vos Post (author's link)

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Sloane, N. J. A. Sequences A097393 and A097394 in "The On-Line Encyclopedia of Integer Sequences."

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Post, Jonathan Vos. "Emirpimes." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein.

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