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 A081238 #{(i,j): mu(i)*mu(j) = -1, 1<=i<=n, 1<=j<=n}, where mu=A008683 (Moebius function). 3
 0, 2, 4, 4, 6, 12, 16, 16, 16, 24, 30, 30, 36, 48, 60, 60, 70, 70, 80, 80, 96, 112, 126, 126, 126, 144, 144, 144, 160, 176, 192, 192, 216, 240, 264, 264, 286, 312, 338, 338, 364, 390, 416, 416, 416, 448, 476, 476, 476, 476, 510, 510, 540, 540, 576, 576, 612, 648 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) + A081239(n) + A081240(n) = n^2; a(n) = a(n-1) iff mu(n) = 0. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..500 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)=16, as there are 6 .. +1 ..... | + - - 0 - + - 0 16 '-1's in the 8x8-square 7 .. -1 ..... | - + + 0 + - + 0 (represented as '-') 8 ... 0 ..... | 0 0 0 0 0 0 0 0. PROG (Haskell) a081238 n = length [() | u <- [1..n], v <- [1..n],                          a008683 u * a008683 v == -1] -- Reinhard Zumkeller, Aug 03 2012 CROSSREFS Cf. A070549. Sequence in context: A224487 A185342 A276985 * A207254 A207403 A208142 Adjacent sequences:  A081235 A081236 A081237 * A081239 A081240 A081241 KEYWORD nonn AUTHOR Reinhard Zumkeller, Mar 11 2003 STATUS approved

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