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Talk:Digital root/Multiplicative digital root

From Rosetta Code

The second task "tabulate MP versus the first five numbers having that MP" is inconsistent with the sample output. Assuming the output values are correct, the task should say "tabulate MDR versus the first five numbers having that MDR", and the "MD" column in the output should be "MDR". --Globules 06:00:08, 20 April 2014 (UTC)

I've fixed that. Values with an MP of 9 seem to be rather large (I stopped looking at 20000000). --Rdm (talk) 08:39, 20 April 2014 (UTC)

I've promoted this to a task. It's got a clear description, and it's got more than 4 implementations in different languages. –Donal Fellows (talk) 15:58, 27 April 2014 (UTC)

The product of decimal digits must be a humble numbers ( 2^a*3^b*5^c*7^d )[edit]

Decimal digits 2..9 are humble numbers
1 does not change anything. 0 stops.

program MultRoot;
{$IFDEF FPC}
{$MODE DELPHI}{$OPTIMIZATION ON,ALL}
{$ENDIF}
{$IFDEF WINDOWS}
{$APPTYPE CONSOLE}
{$ENDIF}
uses
sysutils;
const
//mul digit of 277777788888899 = 4996238671872
lnMax = ln(4996238671873);//ln(High(Uint64));
type
tnm = record
nmNum : Uint64;
nmLnNum : double;
nmPots: array[0..3] of byte;
nmMulRoot,
nmMulPers : Int16;
end;
tHumble = array[0..4679{15540}] of tnm;
var
Humble : tHumble;
idx: Uint32;
 
Procedure QuickSort ( Left, Right : LongInt );
Var
i, j : LongInt;
pivot : Uint64;
tmp : tnm;
Begin
i:=Left;
j:=Right;
pivot := Humble[(Left + Right) shr 1].nmNum;
Repeat
While pivot > Humble[i].nmNum Do inc(i);
While pivot < Humble[j].nmNum Do dec(j);
 
If i<=j Then Begin
tmp:=Humble[i];
Humble[i]:=Humble[j];
Humble[j]:=tmp;
dec(j);
inc(i);
End;
Until i>j;
If Left<j Then QuickSort(Left,j);
If i<Right Then QuickSort(i,Right);
End;
 
function GetMulDigits(n:Uint64):UInt64;
//inserting only numbers without any '0'
var
i,q :Uint64;
begin
i := 1;
repeat
q := n div 10;
i := (n-10*q)*i;
n := q;
until (i= 0) OR (n= 0);
GetMulDigits := i;
end;
 
procedure Insert(prime,NumIdx:Uint32);
var
lnPot,
lnPotSum:double;
potNum : Uint64;
i,j,pot :Uint32;
begin
i := idx+1;
pot := 0;
potNum := 1;
lnPot := ln(prime);
lnPotSum := 0.0;
repeat
inc(pot);
potNum := potNum*prime;
lnPotSum := pot*lnPot;
if lnPotSum>lnMax then
BREAK;
for j := 0 to idx do
begin
//ends in '0' 2^x*5*y //x,y > 0 will stay 0
if (numIdx = 2) AND (Humble[j].nmPots[0]<> 0) then continue;
Humble[i] := Humble[j];
with Humble[i] do
begin
if (Potnum>0) AND (nmLnNum+lnPotSum < lnMax) then
begin
nmLnNum := nmLnNum+lnPotSum;
nmNum := nmNum*potNum;
nmPots[NumIdx] := pot;
nmMulRoot := -1;
nmMulPers := 0;
inc(i);
end;
end;
end;
until false;
idx := i-1;
 
writeln('insert powers of ',prime,' new count ',idx);
end;
 
procedure OutHumble(h:tnm);
var
s : string[23];
n,last : UInt64;
i,p : Uint32;
ch: char;
begin
with h do
begin
write(h.nmMulPers:3,' : ');
n := nmNum;
For i := 0 to 3 do write(nmPots[i]:3);
//creating smallest number which digits multiply to n
setlength(s,23);
//extract '9'
s[1] := ' ';
p:= 2;
while nmPots[1]>1 do
begin
s[p] :=('9');inc(p);
nmPots[1] := nmPots[1]-2;
end;
//'8'
while nmPots[0]>2 do
begin
s[p] :=('8');inc(p);
nmPots[0] := nmPots[0]-3;
end;
//'7'
while nmPots[3]>0 do
begin
s[p] :=('7');inc(p);
nmPots[3] := nmPots[3]-1;
end;
//'6'
while (nmPots[0]>0) AND (nmPots[1]>0) do
begin
s[p] :=('6');inc(p);
nmPots[0] := nmPots[0]-1;
nmPots[1] := nmPots[1]-1;
end;
//'5'
while (nmPots[2]>0)do
begin
s[p] :=('5');inc(p);
nmPots[2] := nmPots[2]-1;
end;
//'4'
while (nmPots[0]>1)do
begin
s[p] :=('4');inc(p);
nmPots[0] := nmPots[0]-2;
end;
//'3'
if (nmPots[1]>0) then
begin
s[p] :=('3');inc(p);
end;
//'2'
if nmPots[0]>0 then
begin
s[p] :=('2');inc(p);
end;
i := 2;
p := p-1;
setlength(s,p);
//swap digits
while i<p do
begin
ch:= s[i];
s[i] := s[p];
s[p] := ch;
inc(i);
dec(p);
end;
if n >= 10 then
write(s,'->',n)
else
write(' ',n);
last := n;
//
n := GetMulDigits(n);
if last <> n then
begin
repeat
write('->',n);
last := n;
n := GetMulDigits(n);
until last=n;
end;
writeln;
end;
end;
var
n,last : Uint64;
i,j : Uint32;
begin
Humble[0].nmNum :=1;
 
Insert(2,0);
Insert(3,1);
Insert(5,2);
Insert(7,3);
//remove numbers with one '0' digit
j:= 0;
For i := 0 to Idx do
begin
if GetMulDigits(Humble[i].nmNum) <> 0 then
Begin
Humble[j] := Humble[i];
inc(j);
end;
end;
idx := j-1;
writeln('remove numbers with "0" digit.Remaining ',idx);
 
QuickSort(0,idx);
 
For i := 0 to Idx do
begin
j :=0;
n := Humble[i].nmNum;
last := n;
n := GetMulDigits(n);
if last <> n then
begin
j := 1;
repeat
inc(j);
last := n;
n := GetMulDigits(n);
until last=n;
end;
Humble[i].nmMulRoot:= n;
Humble[i].nmMulPers:= j;
end;
 
For i := 0 to idx do
OutHumble(Humble[i]);
{$IFDEF WINDOWS}
write(' done. Press <ENTER>');readln;
{$ENDIF}
end.
Whats special about 277777788888899
277,777,788,888,899
 
@TIO.RUN:
//Real time: 0.134 s User time: 0.094 s
insert powers of 2 new count 42
insert powers of 3 new count 595
insert powers of 5 new count 833
insert powers of 7 new count 4679
remove numbers with "0" digit.Remaining 2096
mulpersistance : pot 2,3,5,7 
  0 :   0  0  0  0      1
  0 :   1  0  0  0      2
  0 :   0  1  0  0      3
  0 :   2  0  0  0      4
  0 :   0  0  1  0      5
  0 :   1  1  0  0      6
  0 :   0  0  0  1      7
  0 :   3  0  0  0      8
  0 :   0  2  0  0      9
  2 :   2  1  0  0 26->12->2
  2 :   1  0  0  1 27->14->4
  2 :   0  1  1  0 35->15->5
  2 :   4  0  0  0 28->16->6
  2 :   1  2  0  0 29->18->8
  2 :   0  1  0  1 37->21->2
  2 :   3  1  0  0 38->24->8

....  267777777899999->smallest number with mul dgt of -> humble 2^5*3^11*5^0*7^7  =4668421498272

  6 :   5 11  0  7 267777777899999->4668421498272->74317824->37632->756->210->0
  3 :   6 21  0  1 37889999999999->4686238234944->191102976->0
  3 :   0 13  2  6 355777777999999->4689262665675->1567641600->0
  3 :  31  7  0  0 68888888888999->4696546738176->1097349120->0
  3 :  11  9  0  6 267777778889999->4742523426816->15482880->0
  3 :   0  3  4 10 3555577777777779->4766769826875->10241925120->0
  3 :   2 20  0  3 47779999999999->4783868198172->260112384->0
  3 :  27  6  0  2 77888888888999->4794391461888->334430208->0
  3 :   0  1  9  7 35555555557777777->4825447265625->129024000->0
  3 :  23  5  0  4 267777888888899->4894274617344->130056192->0
  4 :  13  6  0  7 277777778888999->4918172442624->6193152->1620->0
 11 :  19  4  0  6 277777788888899->4996238671872->438939648->4478976->338688->27648->2688->768->336->54->20->0