A066640 - OEIS

%I #17 Nov 18 2024 11:02:27

%S 1,3,5,7,9,11,13,15,17,19,31,33,35,37,39,51,53,55,57,59,71,73,77,79,

%T 91,93,95,97,99,111,113,117,119,131,133,137,139,151,153,155,157,159,

%U 171,173,177,179,191,193,197,199

%N Numbers such that all divisors have only odd digits.

%C Is this sequence infinite? - _Charles R Greathouse IV_, Sep 07 2012

%H Charles R Greathouse IV, <a href="/A066640/b066640.txt">Table of n, a(n) for n = 1..10000</a>

%e 77 = 11 * 7 belongs to this sequence but 75 does not as 25 (with a 2) divides 75.

%t Select[Range[250], And@@OddQ/@Flatten[IntegerDigits/@Divisors[ # ]]&]

%o (PARI) f(n)=vecmin(Vec(Vecsmall(Str(n)))%2)

%o is(n)=fordiv(n,d,if(!f(d),return(0)));1 \\ _Charles R Greathouse IV_, Sep 07 2012

%o (Python)

%o from itertools import islice, count

%o from sympy import divisors

%o def A066640(): return filter(lambda n: all(set(str(m)) <= {'1','3','5','7','9'} for m in divisors(n,generator=True)), count(1,2))

%o A066640_list = list(islice(A066640(),20)) # _Chai Wah Wu_, Nov 22 2021

%Y Subsequence of A014261. A030096 is a subsequence.

%K nonn,base

%O 1,2

%A _Amarnath Murthy_, Dec 28 2001

%E Corrected and extended by _Harvey P. Dale_, Jan 01 2002