A305566 Number of finite sets of relatively prime positive integers > 1 with least common multiple n.

0, 0, 0, 0, 0, 2, 0, 0, 0, 2, 0, 10, 0, 2, 2, 0, 0, 10, 0, 10, 2, 2, 0, 44, 0, 2, 0, 10, 0, 84, 0, 0, 2, 2, 2, 122, 0, 2, 2, 44, 0, 84, 0, 10, 10, 2, 0, 184, 0, 10, 2, 10, 0, 44, 2, 44, 2, 2, 0, 1590, 0, 2, 10, 0, 2, 84, 0, 10, 2, 84, 0, 1156, 0, 2, 10, 10, 2

Offset: 1

Author

Gus Wiseman, Jun 05 2018

Keywords

• nonn

Comments

From Robert Israel, Jun 06 2018: (Start)

a(n) depends only on the prime signature of n.

If n is in A000961, a(n)=0.

If n is in A006881, a(n)=2. (End)

If n = p^k*q, where p and q are distinct primes and k >= 1, then a(n) = 3*4^(k-1)-2^(k-1). - Robert Israel, Jun 07 2018

Examples

			The a(12) = 10 sets:
{3,4},
{2,3,4}, {2,3,12}, {3,4,6}, {3,4,12},
{2,3,4,6}, {2,3,4,12}, {2,3,6,12}, {3,4,6,12},
{2,3,4,6,12}.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000961, A006881, A076078, A181819, A281116, A285572, A290103, A304818, A305563, A305564, A305565, A305567.

Programs

Maple

f:= proc(n) g(sort(map(t -> t[2],ifactors(n)[2]))) end proc:
f(1):= 0:
g:= proc(L) option remember;
  local nL, Cands, nC, Cons, i;
  nL:= nops(L);
  Cands:= [[]];
  for i from 1 to nL do
    Cands:= [seq(seq([op(s),t],t=0..L[i]),s=Cands)];
  od:
  Cands:= remove(t -> max(t)=0, Cands);
  nC:= nops(Cands);
  Cons:= [seq(select(t -> Cands[t][i]=0, {$1..nC}),i=1..nL),
          seq(select(t -> Cands[t][i]=L[i], {$1..nC}), i=1..nL)];
  h(Cons, {$1..nC})
end proc:
h:= proc(Cons, Cands)
  local t,i,Consi, Candsi;
  if Cons = [] then return 2^nops(Cands) fi;
  t:= 0;
  for i from 1 to nops(Cons[1]) do
    Consi:= map(proc(t) if member(Cons[1][i],t) then NULL else t minus Cons[1][1..i-1] fi end proc, Cons[2..-1]);
    if member({},Consi) then next fi;
    Candsi:= Cands minus Cons[1][1..i];
    t:= t + procname(Consi, Candsi)
  od;
  t
end proc:
map(f, [$1..100]); # Robert Israel, Jun 07 2018

Mathematica

Table[Length[Select[Subsets[Rest[Divisors[n]]],And[GCD@@#==1,LCM@@#==n]&]],{n,100}]