OFFSET
1,1
COMMENTS
A304711 lists numbers whose distinct prime indices are pairwise coprime.
The first term divisible by 4 is a(421) = 1092.
LINKS
EXAMPLE
The sequence of terms together with their prime indices begins:
3: {2} 39: {2,6} 78: {1,2,6}
5: {3} 41: {13} 79: {22}
7: {4} 42: {1,2,4} 81: {2,2,2,2}
9: {2,2} 43: {14} 83: {23}
11: {5} 47: {15} 87: {2,10}
13: {6} 49: {4,4} 89: {24}
17: {7} 53: {16} 91: {4,6}
19: {8} 57: {2,8} 97: {25}
21: {2,4} 59: {17} 101: {26}
23: {9} 61: {18} 103: {27}
25: {3,3} 63: {2,2,4} 105: {2,3,4}
27: {2,2,2} 65: {3,6} 107: {28}
29: {10} 67: {19} 109: {29}
31: {11} 71: {20} 111: {2,12}
37: {12} 73: {21} 113: {30}
MATHEMATICA
nn=100;
dat=Select[Range[nn], CoprimeQ@@PrimePi/@First/@FactorInteger[#]&];
facsusing[s_, n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facsusing[Select[s, Divisible[n/d, #]&], n/d], Min@@#>=d&]], {d, Select[s, Divisible[n, #]&]}]];
Select[Range[nn], facsusing[dat, #]=={}&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 02 2020
STATUS
approved