OFFSET
1,3
COMMENTS
The a(n)-th squarefree semiprime is the first divisible by prime(n).
After a(1) = 1, these are the positions of even terms in the list of all squarefree semiprimes A006881.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
rs=First/@FactorInteger[#]&/@Select[Range[100], SquareFreeQ[#]&&PrimeOmega[#]==2&];
Table[Position[rs, i][[1, 1]], {i, Union@@rs}]
CROSSREFS
A005117 lists squarefree numbers.
A115392 is the not necessarily squarefree version.
A166237 gives the first differences of squarefree semiprimes.
A320656 counts factorizations into squarefree semiprimes.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Nov 16 2020
STATUS
approved