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A066640
Numbers such that all divisors have only odd digits.
2
1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 31, 33, 35, 37, 39, 51, 53, 55, 57, 59, 71, 73, 77, 79, 91, 93, 95, 97, 99, 111, 113, 117, 119, 131, 133, 137, 139, 151, 153, 155, 157, 159, 171, 173, 177, 179, 191, 193, 197, 199
OFFSET
1,2
COMMENTS
Is this sequence infinite? - Charles R Greathouse IV, Sep 07 2012
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
77 = 11 * 7 belongs to this sequence but 75 does not as 25 (with a 2) divides 75.
MATHEMATICA
Select[Range[250], And@@OddQ/@Flatten[IntegerDigits/@Divisors[ # ]]&]
PROG
(PARI) f(n)=vecmin(Vec(Vecsmall(Str(n)))%2)
is(n)=fordiv(n, d, if(!f(d), return(0))); 1 \\ Charles R Greathouse IV, Sep 07 2012
(Python)
from itertools import islice, count
from sympy import divisors
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))
A066640_list = list(islice(A066640(), 20)) # Chai Wah Wu, Nov 22 2021
CROSSREFS
Subsequence of A014261.
Sequence in context: A143451 A352547 A014261 * A137507 A061808 A248608
KEYWORD
nonn,base
AUTHOR
Amarnath Murthy, Dec 28 2001
EXTENSIONS
Corrected and extended by Harvey P. Dale, Jan 01 2002
STATUS
approved