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

1,1

Comments

Presumed infinite.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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

Cf. A002113, A116935

Sequence in context: A257035 A128608 A326710 * A222551 A017282 A036304

Adjacent sequences: A144716 A144717 A144718 * A144720 A144721 A144722

Keyword

base,easy,nonn

Author

Reikku Kulon, Sep 19 2008

Status

approved