Emirpimes
المؤلف:
Sloane, N. J. A
المصدر:
Sequences A097393 and A097394 in "The On-Line Encyclopedia of Integer Sequences."
الجزء والصفحة:
...
11-1-2021
1537
Emirpimes
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., 
and 
). 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 
for 
, 2, ... are 0, 10, 90, 898, 7200, 60732, ... (OEIS A097394).
REFERENCES:
Sloane, N. J. A. Sequences A097393 and A097394 in "The On-Line Encyclopedia of Integer Sequences."
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