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%I #37 Sep 24 2023 05:49:05
%S 2,4,6,9,11,13,17,20,23,25,27,30,33,36,39,41,45,49,51,53,56,59,61,65,
%T 67,69,72,75,77,81,83,88,91,94,98,100,102,105,107,111,113,116,119,121,
%U 123,126,129,134,136,138,142,144,147,149,152,155,158,161,163,165,168
%N a(n) = n-th squarefree number plus n-th cubefree number.
%H Harvey P. Dale, <a href="/A160813/b160813.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = A005117(n) + A004709(n).
%F a(n) ~ c*n, where c = zeta(2) + zeta(3) (A347213). - _Amiram Eldar_, Sep 24 2023
%e a(1) = 1+1 = 2.
%e a(4) = 5+4 = 9.
%e a(8) = 11+9 = 20.
%t 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 *)
%Y Cf. A004709, A005117, A046100, A347213.
%K nonn,easy
%O 1,1
%A _Jonathan Vos Post_, Jan 19 2011
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