A201021 Composite numbers whose multiplicative digital root is 7.

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. ~

Links

Table of n, a(n) for n=1..31.

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

Adjacent sequences: A201018 A201019 A201020 * A201022 A201023 A201024

Keyword

nonn,base

Author

Jaroslav Krizek, Nov 25 2011

Status

approved