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A071323
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Alternating sum of all divisors of n; divisors non-decreasing, starting with 1.
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2
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1, -1, -2, 3, -4, -4, -6, -5, 7, -6, -10, -8, -12, -8, -12, 11, -16, -13, -18, -12, -16, -12, -22, -16, 21, -14, -20, -18, -28, -22, -30, -21, -24, -18, -32, 25, -36, -20, -28, -24, -40, -32, -42, -30, -36, -24, -46, -32, 43
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OFFSET
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1,3
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COMMENTS
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a(n)>0 iff n square (iff A000005(n) is even), a(A000290(n))>0;
for primes p: a(p) = 1-p.
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LINKS
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Table of n, a(n) for n=1..49.
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EXAMPLE
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Divisors of 20: {1,2,4,5,10,20} therefore a(20) = 1-2+4-5+10-20 = -12.
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CROSSREFS
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Cf. A000203, A071321, A071324.
Sequence in context: A091860 A181833 A158973 * A071324 A063655 A117248
Adjacent sequences: A071320 A071321 A071322 * A071324 A071325 A071326
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KEYWORD
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sign
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AUTHOR
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Reinhard Zumkeller, May 18 2002
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STATUS
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approved
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