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A109027
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7-almost primes (A046308) whose digit reversal is different and also has 7 prime factors (with multiplicity). "Emirp Tsomla-7.".
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6
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8820, 21240, 21708, 21780, 21920, 23280, 23472, 23625, 23800, 25560, 25584, 25758, 26280, 27432, 27504, 27888, 27900, 28836, 29250, 29403, 29736, 29970, 30492, 34884, 36828, 40338, 40572, 40950, 41976, 42228, 42984, 43659, 43956, 44128
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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 = 7 instance of the series which begins with k = 1 (emirps), k = 2 (emirpimes), k = 3 (emirp tsomla-3 = A109023), k = 4 (emirp tsomla-4 = A109024), k = 5 (emirp tsomla-5 = A109025), k = 6 (emirp tsomla-6 = A109026).
The Mathematica code for this was written by Ray Chandler who extended this sequence. He also has more values.
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REFERENCES
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Jonathan Vos Post, "1066 and All That: Emirp Tsomla-3 and Related Integer Sequences." Forthcoming paper on this sequence.
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LINKS
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Table of n, a(n) for n=1..34.
Eric Weisstein's World of Mathematics, Almost Prime.
Eric Weisstein's World of Mathematics, Emirp.
Eric Weisstein and Jonathan Vos Post, Emirpimes.
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EXAMPLE
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a(20) = 29403 is in this sequence because 29403 = 3^5 * 11^2 is a 7-almost prime and reverse(29403) = 30492 = 2^2 * 3^2 * 7 * 11^2 is also a 7-almost prime.
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MATHEMATICA
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Select[Range[45000], !PalindromeQ[#]&&PrimeOmega[#]==PrimeOmega[ IntegerReverse[ #]] ==7&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 02 2019 *)
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CROSSREFS
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Cf. A046308, A006567, A097393, A109018, A109023-A109026, A109028-A109131.
Sequence in context: A270609 A230335 A183752 * A237761 A186582 A147529
Adjacent sequences: A109024 A109025 A109026 * A109028 A109029 A109030
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KEYWORD
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nonn,base
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AUTHOR
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Jonathan Vos Post, Jun 16 2005
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STATUS
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approved
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