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A201021
Composite numbers whose multiplicative digital root is 7.
0
117, 171, 711, 1711, 7111, 11711, 17111, 71111, 111117, 111171, 111711, 117111, 171111, 711111, 1111117, 1111171, 1711111, 7111111, 11111711, 11117111, 11171111, 11711111, 17111111, 111111117, 111111171, 111111711, 111117111, 111171111, 111711111, 117111111, 171111111
OFFSET
1,1
COMMENTS
Also composite numbers whose product of digits is 7.
Complement of A107693 with respect to A034054. ~
FORMULA
Number 171 is in sequence because 1*7*1=7.
MATHEMATICA
Flatten[Table[Select[FromDigits/@Permutations[PadRight[{7}, n, 1]], CompositeQ], {n, 9}]]//Sort (* Harvey P. Dale, Mar 29 2023 *)
CROSSREFS
Cf. A107693 (primes whose multiplicative digital root is 7), A034054 (numbers whose multiplicative digital root is 7).
Sequence in context: A109023 A272388 A272389 * A112877 A064180 A050245
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 25 2011
STATUS
approved