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 A081240 #{(i,j): mu(i)*mu(j) = 1, 1<=i,j<=n}, where mu=A008683 (Moebius function). 3
 1, 2, 5, 5, 10, 13, 20, 20, 20, 25, 34, 34, 45, 52, 61, 61, 74, 74, 89, 89, 100, 113, 130, 130, 130, 145, 145, 145, 164, 185, 208, 208, 225, 244, 265, 265, 290, 313, 338, 338, 365, 394, 425, 425, 425, 452, 485, 485, 485, 485, 514, 514, 549, 549, 580, 580, 613 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A081238(n) + A081239(n) + a(n) = n^2; a(n) = a(n-1) iff mu(n) = 0. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..520 FORMULA a(n) = |sum(i=1..n, sqrt(mu(i))|^2. - Enrique Pérez Herrero, Jul 30 2012 EXAMPLE n mu(n) ... n: 1 2 3 4 5 6 7 8 - ------ .... |----------------> 1 .. +1 ..... | + - - 0 - + - 0 2 .. -1 ..... | - + + 0 + - + 0 3 .. -1 ..... | - + + 0 + - + 0 4 ... 0 ..... | 0 0 0 0 0 0 0 0 5 .. -1 ..... | - + + 0 + - + 0 a(8)=20, as there are 6 .. +1 ..... | + - - 0 - + - 0 20 '+1's in the 8x8-square 7 .. -1 ..... | - + + 0 + - + 0 (represented as '+') 8 ... 0 ..... | 0 0 0 0 0 0 0 0. MATHEMATICA Table[Abs[Sum[Sqrt[MoebiusMu[i]], {i, 1, n}]]^2, {n, 60}] (* Enrique Pérez Herrero, Jul 30 2012 *) PROG (Haskell) a081240 n = length [() | u <- [1..n], v <- [1..n], a008683 u * a008683 v == 1] -- Reinhard Zumkeller, Aug 03 2012 CROSSREFS Cf. A070548. Sequence in context: A351475 A034387 A349803 * A184443 A238655 A132295 Adjacent sequences: A081237 A081238 A081239 * A081241 A081242 A081243 KEYWORD nonn AUTHOR Reinhard Zumkeller, Mar 11 2003 STATUS approved

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Last modified August 10 00:01 EDT 2024. Contains 375044 sequences. (Running on oeis4.)