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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.
2
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
1,1
COMMENTS
Prime factors counted without multiplicity. - Harvey P. Dale, Nov 29 2014
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000 (corrected by Sean A. Irvine)
EXAMPLE
Reversing 339 = 3*113 gives 933 = 3*311, both with two prime factors.
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 *)
CROSSREFS
Cf. A050699.
Sequence in context: A043147 A043927 A330701 * A105997 A354345 A075288
KEYWORD
nonn,base,nice
AUTHOR
Patrick De Geest, Aug 15 1999
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
STATUS
approved