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A144719 Semiprimes whose factors are decimal palindromes when concatenated, omitting multiples of primes less than 11. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Presumed infinite.
LINKS
EXAMPLE
121 = 11 * 11; 1111 is a palindrome.
4309 = 139 * 31; 13931 is a palindrome.
MATHEMATICA
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 *)
CROSSREFS
Sequence in context: A257035 A128608 A326710 * A222551 A017282 A036304
KEYWORD
base,easy,nonn
AUTHOR
Reikku Kulon, Sep 19 2008
STATUS
approved

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Last modified April 17 05:47 EDT 2024. Contains 371756 sequences. (Running on oeis4.)