OFFSET
1,1
COMMENTS
First differs from A212164 at a(441).
Numbers n such that A050326(n) = 0. - Felix Fröhlich, Oct 04 2017
Includes A246547, and all numbers of the form p^a*q^b where p and q are primes, a >= 1 and b >= 3. - Robert Israel, Oct 10 2017
Also numbers whose prime indices cannot be partitioned into a set of sets. For example, the prime indices of 90 are {1,2,2,3}, and we have sets of sets: {{2},{1,2,3}}, {{1,2},{2,3}}, {{1},{2},{2,3}}, {{2},{3},{1,2}}, so 90 is not in the sequence. - Gus Wiseman, Apr 28 2025
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
120 is not in the sequence because 120 = 2*6*10. 3600 is not in the sequence because 3600 = 2*6*10*30.
MAPLE
N:= 1000: # to get all terms <= N
A:= Vector(N):
A[1]:= 1:
for n from 2 to N do
if numtheory:-issqrfree(n) then
S:= [$1..N/n]; T:= n*S; A[T]:= A[T]+A[S]
fi;
od:
select(t -> A[t]=0, [$1..N]); # Robert Israel, Oct 10 2017
MATHEMATICA
nn=500;
sqfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[sqfacs[n/d], Min@@#>d&]], {d, Select[Rest[Divisors[n]], SquareFreeQ]}]];
Select[Range[nn], Length[sqfacs[#]]===0&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Oct 03 2017
STATUS
approved
