A050702 Nonprime numbers n such that n and n-reversed (<>n and no leading zeros) have the same number of prime factors and these prime factors (palindromes allowed here) are also reversals of each other.

26, 39, 62, 93, 143, 169, 187, 226, 286, 339, 341, 622, 682, 781, 933, 961, 1089, 1177, 1243, 1313, 1469, 1573, 1717, 2042, 2062, 2066, 2178, 2206, 2402, 2426, 2446, 2462, 2486, 2602, 2626, 2642, 3063, 3093, 3099, 3131, 3309, 3421, 3603, 3639, 3669, 3693, 3737, 3751, 3903, 3939, 3963, 4084

Offset: 1

Author

Patrick De Geest, Aug 15 1999

Keywords

• nonn
• base
• nice

Comments

Prime factors counted without multiplicity. - Harvey P. Dale, Nov 29 2014

Examples

			Reversing 339 = 3*113 gives 933 = 3*311, both with two prime factors.
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000 (corrected by Sean A. Irvine)

Crossrefs

Cf. A050699.

Programs

Mathematica

d[n_]:=IntegerDigits[n]; f[n_]:=First/@FactorInteger[n]; Select[Range[4100],!PrimeQ[#]&&Reverse/@d[f[#]]==d[f[x=FromDigits[Reverse[d[#]]]]]&&#!=x&](* Jayanta Basu, May 31 2013 *)
snpfQ[n_]:=Module[{pfn=Transpose[FactorInteger[n]][[1]],idn = IntegerDigits[ n], revn, pfrev, revpfrev},revn = FromDigits[ Reverse[idn]];pfrev=Transpose[ FactorInteger[ revn]][[1]]; revpfrev =FromDigits[Reverse[IntegerDigits[#]]]&/@pfrev;!PrimeQ[n]&& Last[ IntegerDigits[ n]] != 0&&revn!=n&&Length[pfn]==Length[pfrev]&&Union[pfn] == Union[ revpfrev]]; Select[ Range[ 4200], snpfQ] (* Harvey P. Dale, Nov 29 2014 *)

Extensions

More terms from Naohiro Nomoto, Apr 03 2001

Corrected by Vincenzo Librandi, Feb 03 2014

Definition clarified by Harvey P. Dale, Nov 29 2014