A144719 Semiprimes whose factors are decimal palindromes when concatenated, omitting multiples of primes less than 11.
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
Offset: 1
Examples
121 = 11 * 11; 1111 is a palindrome. 4309 = 139 * 31; 13931 is a palindrome.
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Programs
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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 *)
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