%I #40 Feb 13 2017 20:20:25
%S 4,14,22,27,39,41,72,89,93,98,114,122,127,139,141,172,189,193,198,212,
%T 217,221,249,266,271,277,294,319,333,338,346,364,379,383,391,397,411,
%U 429,436,463,492,626,634,643,662,677,712,721,727,739,767,772,776,793
%N Numbers with multiplicative digital root value 4.
%H Robert Israel, <a href="/A034051/b034051.txt">Table of n, a(n) for n = 1..5000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/MultiplicativeDigitalRoot.html">Multiplicative Digital Root</a>
%H <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a>.
%p mdr:= proc(n) option remember;
%p if n < 10 then return(n) fi;
%p procname(convert(convert(n,base,10),`*`))
%p end proc:
%p select(mdr=4, [$1..10^5]); # _Robert Israel_, Oct 19 2015
%t Select[Range@ 800, FixedPoint[Times @@ IntegerDigits@ # &, #] == 4 &] (* _Michael De Vlieger_, Oct 19 2015 *)
%o (PARI) t(n) = {while(n>9, n=prod(i=1, #n=digits(n), n[i])); n};
%o for(n=0, 1e4, if(t(n) == 4, print1(n", "))); \\ _Altug Alkan_, Oct 19 2015
%Y Cf. A031347.
%Y Cf. A034048, A002275, A034049, A034050, A034051, A034052, A034053, A034054, A034055, A034056 (numbers having multiplicative digital roots 0-9).
%K nonn,base,easy
%O 1,1
%A _Patrick De Geest_, Sep 15 1998
%E Incorrect formula removed by _Martin Renner_, Oct 19 2015