The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A034054 Numbers with multiplicative digital root value 7. 16
 7, 17, 71, 117, 171, 711, 1117, 1171, 1711, 7111, 11117, 11171, 11711, 17111, 71111, 111117, 111171, 111711, 117111, 171111, 711111, 1111117, 1111171, 1111711, 1117111, 1171111, 1711111, 7111111, 11111117, 11111171, 11111711, 11117111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers with one 7, and zero or more 1s. - Daniel Forgues, Oct 09 2011 LINKS Eric Weisstein's World of Mathematics, Multiplicative Digital Root FORMULA There are n(n+1)/2 elements up to 10^n, so a(n) is about 10^sqrt(2n). MATHEMATICA Sort[Flatten[Table[FromDigits/@Permutations[Join[{7}, PadRight[{}, n, 1]]], {n, 0, 10}]]] (* Harvey P. Dale, Jul 20 2015 *) PROG (PARI) t(k)=while(k>9, k=prod(i=1, #k=digits(k), k[i])); k for(n=1, 1e8, if(t(n) == 7, print1(n, ", "))); \\ Altug Alkan, Oct 22 2015 CROSSREFS Cf. A031347. Cf. A034048, A002275, A034049, A034050, A034051, A034052, A034053, A034054, A034055, A034056 (numbers having multiplicative digital roots 0-9). Sequence in context: A051809 A254500 A242907 * A120876 A216073 A086870 Adjacent sequences:  A034051 A034052 A034053 * A034055 A034056 A034057 KEYWORD nonn,base,easy AUTHOR Patrick De Geest, Sep 15 1998 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 15 13:37 EDT 2021. Contains 342977 sequences. (Running on oeis4.)