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A050702
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Nonprime numbers n such that n and n-reversed (<>n and no leading zeros) have the same number of prime factors and these prime factors (palindromes allowed here) are also reversals of each other.
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2
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26, 39, 62, 93, 143, 169, 187, 226, 286, 339, 341, 622, 682, 781, 933, 961, 1089, 1177, 1243, 1313, 1469, 1573, 1717, 2042, 2062, 2066, 2178, 2206, 2402, 2426, 2446, 2462, 2486, 2602, 2626, 2642, 3063, 3093, 3099, 3131, 3309, 3421, 3603, 3639, 3669, 3693, 3737, 3751, 3903, 3939, 3963, 4084
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OFFSET
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1,1
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COMMENTS
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Prime factors counted without multiplicity. - Harvey P. Dale, Nov 29 2014
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LINKS
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EXAMPLE
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Reversing 339 = 3*113 gives 933 = 3*311, both with two prime factors.
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MATHEMATICA
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d[n_]:=IntegerDigits[n]; f[n_]:=First/@FactorInteger[n]; Select[Range[4100], !PrimeQ[#]&&Reverse/@d[f[#]]==d[f[x=FromDigits[Reverse[d[#]]]]]&&#!=x&](* Jayanta Basu, May 31 2013 *)
snpfQ[n_]:=Module[{pfn=Transpose[FactorInteger[n]][[1]], idn = IntegerDigits[ n], revn, pfrev, revpfrev}, revn = FromDigits[ Reverse[idn]]; pfrev=Transpose[ FactorInteger[ revn]][[1]]; revpfrev =FromDigits[Reverse[IntegerDigits[#]]]&/@pfrev; !PrimeQ[n]&& Last[ IntegerDigits[ n]] != 0&&revn!=n&&Length[pfn]==Length[pfrev]&&Union[pfn] == Union[ revpfrev]]; Select[ Range[ 4200], snpfQ] (* Harvey P. Dale, Nov 29 2014 *)
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CROSSREFS
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KEYWORD
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nonn,base,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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