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
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