A066640 Numbers such that all divisors have only odd digits.

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

Adjacent sequences: A066637 A066638 A066639 * A066641 A066642 A066643

Keyword

nonn,base

Author

Amarnath Murthy, Dec 28 2001

Extensions

Corrected and extended by Harvey P. Dale, Jan 01 2002

Status

approved