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A109023
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3-almost primes (A014612) whose digit reversal is different and also has 3 prime factors (with multiplicity).
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11
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117, 147, 165, 244, 246, 285, 286, 290, 338, 366, 369, 406, 418, 425, 435, 438, 442, 475, 498, 506, 507, 508, 524, 534, 539, 548, 561, 574, 582, 604, 605, 609, 628, 642, 663, 670, 682, 705, 711, 741, 759, 805, 814, 826, 833, 834, 845, 890, 894, 906, 935
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OFFSET
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1,1
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COMMENTS
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This sequence is the k = 3 instance of the series which begins with k = 1, k = 2.
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REFERENCES
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W. W. R. Ball and H. S. M. Coxeter, Mathematical Recreations and Essays, 13th ed. New York: Dover, pp. 14-15, 1987.
J. Edalj, Problem 1622. L'Intermédiaire des Mathématiciens, 16, 34, 1909.
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LINKS
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J. Jonesco, Query 1622, L'Intermédiaire des Mathématiciens, 200, Tome VI, 1899.
Eric Weisstein's World of Mathematics, Emirp.
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EXAMPLE
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1066 is in this sequence because 1066 = 2 * 13 * 41, making it a 3-almost prime and reverse(1066) = 6601 = 7 * 23 * 41, also a 3-almost prime.
2001 is in this sequence because 2001 = 3 * 23 * 29 and reverse(2001) = 1002 = 2 * 3 * 167.
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MATHEMATICA
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Select[Range[1000], PrimeOmega[#]==3&&PrimeOmega[FromDigits[Reverse[IntegerDigits[#]]]]==3&&!PalindromeQ[#]&] (* James C. McMahon, Mar 06 2024 *)
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PROG
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(PARI) is(n) = {
my(r = fromdigits(Vecrev(digits(n))));
n!=r && bigomega(n) == 3 && bigomega(r) == 3
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CROSSREFS
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Cf. A006567, A097393, A109018, A109024, A109025, A109026, A109027, A109028, A109029, A109030, A109031.
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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