The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 13 17:32 EDT 2024. Contains 373391 sequences. (Running on oeis4.)