A062680 - OEIS

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A062680

Composite numbers whose divisors (except 1) all contain the digit 9.

1691, 2291, 3629, 5191, 5539, 5597, 6931, 7391, 7921, 7961, 8497, 8791, 9101, 9329, 9409, 9481, 9671, 9701, 10981, 10991, 11269, 13129, 13891, 14239, 15089, 15931, 15941, 16999, 17197, 17309, 17879, 17951, 17993, 18091, 18449, 18829, 18943

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OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

EXAMPLE

7961 has divisors 19, 419 and 7961, all of which contain the digit 9.

MATHEMATICA

fQ[n_] := Union[Drop[Last /@ Sort /@ IntegerDigits[ Divisors[ n]], 1]] == {9}; Select[ Range[ 19110], fQ[ # ] == True && ! PrimeQ[ # ] &] (* Zak Seidov and Robert G. Wilson v, May 17 2005 *)

fQ[n_, dgt_] := Union[ MemberQ[#, dgt] & /@ IntegerDigits@ Rest@ Divisors@ n][[1]]; Select[ Range[2, 19110], !PrimeQ[#] && fQ[#, 9] &] (* Robert G. Wilson v, Jun 11 2014 *)

PROG

(Magma) [k:k in [2..20000]| not IsPrime(k) and forall{d:d in Set(Divisors(k)) diff {1}| 9 in Intseq(d)}]; // Marius A. Burtea, Nov 07 2019

CROSSREFS

Composite members of A062679.

Cf. A062653, A062664, A062667, A062668, A062669, A062670, A062671, A062672, A062673, A062674, A062675, A062676, A062677, A062678.

Sequence in context: A020241 A065903 A204488 * A251291 A120564 A237533

Adjacent sequences: A062677 A062678 A062679 * A062681 A062682 A062683

KEYWORD

base,easy,nonn

AUTHOR

Erich Friedman, Jul 04 2001

EXTENSIONS

Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, May 16 2007

STATUS

approved