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A046446
Nonprimes whose prime factors contain only odd digits.
0
1, 9, 15, 21, 25, 27, 33, 35, 39, 45, 49, 51, 55, 57, 63, 65, 75, 77, 81, 85, 91, 93, 95, 99, 105, 111, 117, 119, 121, 125, 133, 135, 143, 147, 153, 155, 159, 165, 169, 171, 175, 177, 185, 187, 189, 195, 209, 213, 217, 219, 221, 225, 231, 237, 243, 245, 247, 255
OFFSET
1,2
EXAMPLE
247 = 13 * 19; 1, 3 and 9 are odd digits.
MAPLE
isA046446 := proc(n)
if not isprime(n) then
fset := numtheory[factorset](n) ;
for f in fset do
convert(convert(f, base, 10), set) ;
if % intersect {0, 2, 4, 6, 8} <> {} then
return false;
end if;
end do:
true ;
else
false;
end if;
end proc:
for n from 1 to 260 do
if isA046446(n) then
printf("%d, ", n) ;
end if;
end do: # R. J. Mathar, Oct 02 2018
MATHEMATICA
Select[Range[255], ! PrimeQ[#] && And @@ OddQ[Union[Flatten[IntegerDigits[First /@ FactorInteger[#]]]]] &] (* Jayanta Basu, Jun 24 2013 *)
CROSSREFS
Subsequence of A014076.
Sequence in context: A067800 A155474 A100819 * A046350 A225438 A175076
KEYWORD
nonn,easy,base
AUTHOR
Patrick De Geest, Jul 15 1998
EXTENSIONS
Definition clarified by Harvey P. Dale, Jul 07 2018
STATUS
approved