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A160813
a(n) = n-th squarefree number plus n-th cubefree number.
1
2, 4, 6, 9, 11, 13, 17, 20, 23, 25, 27, 30, 33, 36, 39, 41, 45, 49, 51, 53, 56, 59, 61, 65, 67, 69, 72, 75, 77, 81, 83, 88, 91, 94, 98, 100, 102, 105, 107, 111, 113, 116, 119, 121, 123, 126, 129, 134, 136, 138, 142, 144, 147, 149, 152, 155, 158, 161, 163, 165, 168
OFFSET
1,1
LINKS
FORMULA
a(n) = A005117(n) + A004709(n).
a(n) ~ c*n, where c = zeta(2) + zeta(3) (A347213). - Amiram Eldar, Sep 24 2023
EXAMPLE
a(1) = 1+1 = 2.
a(4) = 5+4 = 9.
a(8) = 11+9 = 20.
MATHEMATICA
Module[{nn=100, sf, cf, len}, sf=Select[Range[nn], SquareFreeQ]; cf=Select[ Range[ nn], Max[FactorInteger[#][[All, 2]]]<3&]; len=Min[ Length[ sf], Length[cf]]; Total/@Thread[{Take[sf, len], Take[cf, len]}]] (* Harvey P. Dale, Oct 01 2019 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Jan 19 2011
STATUS
approved