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 A285881 Number of even squarefree numbers <= n. 1
 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 LINKS Table of n, a(n) for n=1..85. Eric Weisstein's World of Mathematics, Squarefree FORMULA G.f.: Sum_{k>=1} x^A039956(k)/(1 - x). a(n) ~ 2*n/Pi^2. MATHEMATICA Table[Sum[Boole[EvenQ[k] && SquareFreeQ[k]], {k, 1, n}], {n, 85}] nmax = 85; Rest[CoefficientList[Series[Sum[Boole[EvenQ[k] && MoebiusMu[k]^2 == 1] x^k/(1 - x), {k, 1, nmax}], {x, 0, nmax}], x]] PROG (Python) from sympy.ntheory.factor_ import core def a(n): return sum([1 for k in range(1, n + 1) if k%2==0 and core(k)==k]) # Indranil Ghosh, Apr 28 2017 CROSSREFS Cf. A005117, A008683, A013928, A039956, A285879. Sequence in context: A169990 A055679 A056172 * A091373 A197637 A235492 Adjacent sequences: A285878 A285879 A285880 * A285882 A285883 A285884 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Apr 27 2017 STATUS approved

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Last modified May 29 13:10 EDT 2024. Contains 372940 sequences. (Running on oeis4.)