OFFSET
1,1
COMMENTS
If n belongs to the sequence also n*10^k does.
Two concatenations are considered different when one of them is not a permutation of the other. E.g.: (6,2,22,5) and (6,22,2,5) are not different.
LINKS
Paolo P. Lava, Table of n, a(n) for n = 1..100
EXAMPLE
Only 2 or 3 different concatenations.
Two different concatenations:
92736 = concat(9*2*736) and 92736 / (9*2*736) = 7;
92736 = concat(92*7*36) and 92736 / (92*7*36) = 4.
Three different concatenations:
23184 = concat(2,3,184) and 23184 / (2*3*184) = 21;
23184 = concat(23,1,84) and 23184 / (23*1*84) = 12;
23184 = concat(23,18,4) and 23184 / (23*18*4) = 14.
The six concatenations of 111111 are excluded because they are basically just one: 1*11*111; 1*111*11; 11*1*111; 11*111*1; 111*1*11; 111*11*1 and 111111 / (1*11*111) = 91.
MAPLE
with(numtheory); P:=proc(q) local a, ab, b, c, i, j, k, m, n, v, w;
v:=array(1..10, 1..3); w:=[]; for n from 1 to q do j:=0;
for i from 1 to ilog10(n) do c:=(n mod 10^i); ab:=trunc(n/10^i);
for k from 1 to ilog10(ab) do a:=trunc(ab/10^k); b:=ab-a*10^k;
if a*b*c>0 then if type(n/(a*b*c), integer) then j:=j+1;
w:=sort([a, b, c]); for m from 1 to 3 do v[j, m]:=w[m]; od;
for m from 1 to j-1 do if v[m, 1]=v[j, 1] and v[m, 2]=v[j, 2] and v[m, 3]=v[j, 3]
then j:=j-1; break; fi; od; fi; fi; od; od;
if j>1 then print(n); fi; od; end: P(10^9);
MATHEMATICA
fQ[n_] := Block[{id = IntegerDigits@ n}, lng = Length@ id; t = Times @@@ Union[Sort /@ Partition[ Flatten@ Table[{FromDigits@ Take[id, {1, i}], FromDigits@ Take[id, {i + 1, j}], FromDigits@ Take[id, {j + 1, lng}]}, {i, 1, lng - 2}, {j, i + 1, lng - 1}], 3]]; Count[IntegerQ /@ (n/t), True] > 1]; k = 100; lst = {}; While[k < 1000001, If[fQ@ k, AppendTo[lst, k]]; k++]; lst (* Robert G. Wilson v, Apr 09 2015 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, Apr 01 2015
STATUS
approved