OFFSET
1,2
COMMENTS
EXAMPLE
The sequence of terms together with their prime indices begins:
1: {}
2: {1}
6: {1,2}
30: {1,2,3}
42: {1,2,4}
210: {1,2,3,4}
330: {1,2,3,5}
390: {1,2,3,6}
462: {1,2,4,5}
510: {1,2,3,7}
546: {1,2,4,6}
714: {1,2,4,7}
798: {1,2,4,8}
2310: {1,2,3,4,5}
2730: {1,2,3,4,6}
3570: {1,2,3,4,7}
3990: {1,2,3,4,8}
4290: {1,2,3,5,6}
4830: {1,2,3,4,9}
5610: {1,2,3,5,7}
MATHEMATICA
hwt[n_]:=Total[Cases[FactorInteger[n], {p_, k_}:>PrimePi[p] k]];
Select[Range[1000], SquareFreeQ[#]&&Union[hwt/@Divisors[#]]==Range[0, hwt[#]]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, May 30 2019
STATUS
approved