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A046451
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Semiprimes whose prime factors, when concatenated, yield a palindrome.
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1
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4, 9, 25, 39, 49, 69, 119, 121, 129, 159, 219, 249, 259, 329, 339, 403, 469, 669, 679, 1207, 1329, 1589, 1703, 2319, 2321, 2359, 2649, 2701, 3039, 3421, 3503, 3629, 3639, 3899, 4303, 4607, 4839, 5603, 5739, 6209, 6401, 6979, 7269, 7663, 7819, 8203, 8519
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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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3899 = 7 * 557 -> 7557 is palindromic.
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MATHEMATICA
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d[n_] := IntegerDigits[n]; co[n_, k_] := Nest[Flatten[d[{#, n}]] &, n, k - 1]; Select[Range[8520], PrimeOmega[#] == 2 && Reverse[x = Flatten[d[co @@@ FactorInteger[#]]]] == x &] (* Jayanta Basu, Jun 26 2013 *)
Select[Range[9000], PrimeOmega[#]==2&&PalindromeQ[FromDigits[ Flatten[ IntegerDigits/@FactorInteger[#][[All, 1]]]]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Mar 19 2020 *)
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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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