A051809 Numbers with nonzero multiplicative digital root 7.

7, 17, 70, 71, 107, 117, 170, 171, 257, 275, 527, 572, 700, 701, 710, 711, 725, 752, 1007, 1017, 1070, 1071, 1107, 1117, 1170, 1171, 1257, 1275, 1527, 1572, 1700, 1701, 1710, 1711, 1725, 1752, 2057, 2075, 2157, 2175

Offset: 1

Author

Dan Hoey, Dec 09 1999

Keywords

• nonn
• easy
• base

Links

• Index entries for 10-automatic sequences.

Crossrefs

Part of histogram of A051802.

Programs

Mathematica

Select[Range[2500],NestWhile[Times@@(IntegerDigits[#]/.(0->1))&,#,#>9&] == 7&] (* Harvey P. Dale, Jan 18 2019 *)

Formula

A051802^-1(7)