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A050700
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Composite numbers n smaller than their decimal reverse but having the same number of prime factors.
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3
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15, 26, 39, 49, 58, 115, 117, 122, 123, 126, 129, 143, 147, 155, 158, 159, 165, 169, 177, 178, 183, 185, 187, 203, 205, 225, 226, 244, 246, 265, 285, 286, 289, 294, 314, 315, 319, 326, 327, 329, 335, 338, 339, 355, 366, 369, 394, 398, 406, 415, 418, 425
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(n)=143 -> a(n)-reversed=341 gives pair (143,341) of which only the smaller value 143 is in this sequence.
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MATHEMATICA
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rev[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; Select[Range[425], !PrimeQ[#]&&PrimeOmega[#]==PrimeOmega[x=rev[#]]&&#<x&] (* Jayanta Basu, May 31 2013 *)
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PROG
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(PARI) is(n)=my(r=fromdigits(Vecrev(digits(n)))); n<r && !isprime(n) && !isprime(r) && bigomega(n)==bigomega(r) \\ Charles R Greathouse IV, Oct 17 2018
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CROSSREFS
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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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