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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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Last modified November 18 14:15 EST 2017. Contains 294893 sequences.