A160813 a(n) = n-th squarefree number plus n-th cubefree number.

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

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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

Cf. A004709, A005117, A046100, A347213.

Sequence in context: A189930 A184627 A203988 * A247515 A186220 A285075

Adjacent sequences: A160810 A160811 A160812 * A160814 A160815 A160816

Keyword

nonn,easy

Author

Jonathan Vos Post, Jan 19 2011

Status

approved