A372146 The smallest number k for which exactly n of its divisors are digitally balanced numbers in base 3 (A049354).

1, 11, 105, 420, 924, 2772, 6240, 4620, 18480, 13860, 55440, 69300, 120120, 180180, 240240, 360360, 514800, 720720, 1029600, 1801800, 2162160, 2522520, 2282280, 5045040, 7207200, 4564560, 6846840, 12612600, 15135120, 11411400, 20540520, 29343600, 22822800, 49729680

Offset: 0

Author

Marius A. Burtea, May 23 2024

Keywords

• nonn
• base

Examples

			Since A049354(1) = 11 it follows that a(0) = 1.
The numbers 2 through 10 have no divisors in A049354 and A049354(1) = 11 = 102_3, so a(1) = 11.
105 has only two divisors in A049354, 15 = A049354(2) and 21 = A049354(4) and is the smallest with exactly two divisors in A049354, so a(2) = 105.
		

Crossrefs

Cf. A049354, A357035.

Programs

Magma

bal:=func; a:=[]; for n in [0..34] do k:=1; while #[d:d in Divisors(k)|bal(d)] ne n do k:=k+1; end while; Append(~a,k); end for; a;

Maple

N:= 15: # for terms before the first term >= 3^(N+1)
db:= proc(n) option remember; local L,d,m;
  L:= convert(n,base,3);
  d:= nops(L);
  d mod 3 = 0 and 3*numboccur(0,L) = d and 3*numboccur(1,L) = d
end proc:
W:= Vector(3^(N+1),datatype=integer[4]):
for d from 3 to N by 3 do
  for t from 3^(d-1) to 3^d-1 do
    if db(t) then
          J:= [seq(i, i=t..3^(N+1), t)];
          W[J]:= W[J] +~ 1;
    fi
od od:
M:= max(W):
V:= Array(0..M): count:= 0:
for i from 1 to 3^(N+1) while count < M+1 do
  if V[W[i]] = 0 then V[W[i]]:= i; count:= count+1 fi;
od:
L:= convert(V,list):
if not member(0,L,'m') then m:= M+2 fi:
L[1..m-1]; # Robert Israel, Jun 03 2024

Mathematica

balQ[n_, b_] := balQ[n, b] = MinMax@ Differences@ DigitCount[n, b] == {0, 0}; f[n_] := DivisorSum[n, 1 &, balQ[#, 3] &]; seq[len_, nmax_] := Module[{s = Table[0, {len}], c = 0, n = 1, i}, While[c < len && n < nmax, i = f[n] + 1; If[i <= len && s[[i]] == 0, c++; s[[i]] = n]; n++]; s]; seq[12, 10^5] (* Amiram Eldar, Jun 03 2024 *)