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A190223
Numbers all of whose divisors are numbers whose decimal digits are noncomposite numbers (1,2,3,5,7).
2
1, 2, 3, 5, 7, 11, 13, 15, 17, 21, 22, 23, 25, 31, 33, 35, 37, 51, 53, 55, 71, 73, 75, 77, 111, 113, 115, 121, 125, 127, 131, 137, 151, 155, 157, 173, 175, 211, 213, 217, 221, 223, 227, 231, 233, 251, 253, 257, 271, 275, 277, 311, 313, 317, 331, 337, 353
OFFSET
1,2
COMMENTS
Subset of A001742.
All terms are obviously odd except for 2 and numbers of the form 2*A004022(k). - Harvey P. Dale, May 28 2014 (corrected by Iain Fox, Sep 03 2020)
LINKS
Iain Fox, Table of n, a(n) for n = 1..10000 (first 1000 terms from G. C. Greubel)
EXAMPLE
Number 115 is in sequence because all divisors of 115 (1, 5, 23, 115) are numbers whose decimal digits are noncomposite numbers (1,2,3,5,7).
MATHEMATICA
ncnQ[n_]:=Module[{digs=Union[Flatten[IntegerDigits/@Divisors[n]]]}, Complement[ digs, {1, 2, 3, 5, 7}]=={}]; Select[ Range[ 400], ncnQ] (* Harvey P. Dale, May 28 2014 *)
PROG
(PARI) is(k) = fordiv(k, d, if(setminus(vecsort(digits(d), , 8), [1, 2, 3, 5, 7]) != [], return(0))); 1 \\ Iain Fox, Dec 28 2017
CROSSREFS
Supersequence: A001742.
Sequence in context: A187731 A182140 A240960 * A086070 A117093 A062063
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, May 06 2011
EXTENSIONS
More terms from Harvey P. Dale, May 28 2014
STATUS
approved