A324763 Number of maximal subsets of {2...n} containing no prime indices of the elements.

1, 1, 2, 2, 2, 3, 6, 6, 6, 6, 10, 10, 16, 16, 16, 16, 24, 24, 48, 48, 48, 48, 84, 84, 84, 84, 84, 84, 144, 144, 228, 228, 228, 228, 228, 228, 420, 420, 420, 420, 648, 648, 1080, 1080, 1080, 1080, 1800, 1800, 1800, 1800, 1800, 1800, 3600, 3600, 3600, 3600, 3600

Offset: 1

Author

Gus Wiseman, Mar 17 2019

Keywords

• nonn

Comments

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

Examples

			The a(1) = 1 through a(9) = 6 subsets:
  {}  {2}  {2}  {2,4}  {3,4}    {2,4,5}  {2,4,5}  {2,4,5,8}  {2,4,5,8}
           {3}  {3,4}  {2,4,5}  {3,4,6}  {2,5,7}  {2,5,7,8}  {2,5,7,8}
                                {4,5,6}  {3,4,6}  {3,4,6,8}  {3,4,6,8,9}
                                         {3,6,7}  {3,6,7,8}  {3,6,7,8,9}
                                         {4,5,6}  {4,5,6,8}  {4,5,6,8,9}
                                         {5,6,7}  {5,6,7,8}  {5,6,7,8,9}
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..100

Crossrefs

The non-maximal version is A324742.

The version for subsets of {1...n} is A324741.

An infinite version is A304360.

Cf. A076078, A084422, A085945, A112798, A276625, A306844, A324764.

Cf. A324695, A324743, A324751, A324756, A324758, A324762.

Programs

Mathematica

maxim[s_]:=Complement[s,Last/@Select[Tuples[s,2],UnsameQ@@#&&SubsetQ@@#&]];
Table[Length[maxim[Select[Subsets[Range[2,n]],Intersection[#,PrimePi/@First/@Join@@FactorInteger/@#]=={}&]]],{n,10}]

PARI

pset(n)={my(b=0, f=factor(n)[, 1]); sum(i=1, #f, 1<<(primepi(f[i])))}
a(n)={my(p=vector(n-1, k, pset(k+1)>>1), d=0); for(i=1, #p, d=bitor(d, p[i]));
my(ismax(b)=my(e=0); forstep(k=#p, 1, -1, if(bittest(b,k), e=bitor(e,p[k]), if(!bittest(e,k) && !bitand(p[k], b), return(0)) )); 1);
((k, b)->if(k>#p, ismax(b), my(f=!bitand(p[k], b)); if(!f || bittest(d, k), self()(k+1, b)) + if(f, self()(k+1, b+(1<Andrew Howroyd, Aug 26 2019

Extensions

Terms a(16) and beyond from Andrew Howroyd, Aug 26 2019