OFFSET
1,1
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000
David A. Corneth, PARI program
EXAMPLE
19606 = 2 * 9803 upside-down is 90961 = 13 * 6997.
MAPLE
UpsideDown := proc(n) local dgs, a, i ; dgs := convert(n, base, 10) ; a := [] ; for i from 1 to nops(dgs) do if op(i, dgs) = 6 then a := [9, op(a)] ; elif op(i, dgs) = 9 then a := [6, op(a)] ; else a := [op(i, dgs), op(a)] ; fi; od: add(op(i, a)*10^(i-1), i=1..nops(a)) ; end: isA054047 := proc(n) local dgs, i ; dgs := convert(n, base, 10) ; for i from 1 to nops(dgs) do if not op(i, dgs) in {0, 1, 6, 8, 9} then RETURN(false) : fi; od: RETURN(true) ; end: isA001358 := proc(n) if numtheory[bigomega](n) = 2 then true; else false; fi; end: isA119738 := proc(n) if isA001358(n) and isA054047(n) then isA001358(UpsideDown(n)) ; else false ; fi; end: for n from 1 to 12000 do if isA119738(n) then printf("%a, ", n) ; fi; od: # R. J. Mathar, Sep 09 2008
MATHEMATICA
Select[Range[8611], ContainsOnly[IntegerDigits[#], {0, 1, 6, 8, 9}]&&PrimeOmega[#]==2&&PrimeOmega[FromDigits[Reverse[IntegerDigits[#]]/.{6->9, 9->6}]]==2&] (* James C. McMahon, Sep 18 2024 *)
PROG
(PARI) \\ See Corneth link. David A. Corneth, Sep 05 2020
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Jonathan Vos Post, Jun 15 2006
EXTENSIONS
8186 inserted by R. J. Mathar, Sep 09 2008
STATUS
approved