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A144719
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Semiprimes whose factors are decimal palindromes when concatenated, omitting multiples of primes less than 11.
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2
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121, 403, 1207, 1243, 1703, 2321, 2701, 3421, 3503, 3629, 4043, 4061, 4069, 4121, 4247, 4303, 4309, 4607, 5603, 6109, 6401, 7663, 8203, 8921, 9329, 9703, 9707, 9943, 10001, 10021, 10187, 10201, 12223, 12283, 12709, 13129, 13801, 14921, 15007
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OFFSET
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1,1
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COMMENTS
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Presumed infinite.
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LINKS
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EXAMPLE
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121 = 11 * 11; 1111 is a palindrome.
4309 = 139 * 31; 13931 is a palindrome.
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MATHEMATICA
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spdpQ[n_]:=Module[{fi=FactorInteger[n][[All, 1]]}, PrimeOmega[n]==2&&Min[ fi]>10 &&AnyTrue[{FromDigits[Flatten[IntegerDigits/@fi]], FromDigits[ Flatten[ IntegerDigits/@Reverse[fi]]]}, PalindromeQ]]; Select[Range[ 15100], spdpQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 12 2020 *)
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CROSSREFS
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KEYWORD
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base,easy,nonn
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AUTHOR
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STATUS
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approved
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