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A068762
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Alternating sum sigma(1)-sigma(2)+sigma(3)-sigma(4)+...+((-1)^(n+1))*sigma(n).
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3
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1, -2, 2, -5, 1, -11, -3, -18, -5, -23, -11, -39, -25, -49, -25, -56, -38, -77, -57, -99, -67, -103, -79, -139, -108, -150, -110, -166, -136, -208, -176, -239, -191, -245, -197, -288, -250, -310, -254, -344, -302, -398, -354, -438, -360, -432, -384, -508, -451, -544, -472, -570, -516, -636, -564, -684, -604
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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FORMULA
| a(n) = sum((-1)^(k+1)*sigma(k), k=1..n)
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EXAMPLE
| a(3) = sigma(1) - sigma(2) + sigma(3) = 1 - 3 + 4 = 2.
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PROG
| (PARI) a068762(m)=local(s, n); s=0; for(n=1, m, if(n%2==0, s=s-sigma(n), s=s+sigma(n)); print1(s, ", "))
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CROSSREFS
| Cf. A000203, A067931.
Sequence in context: A128932 A071950 A165922 * A155679 A159580 A021448
Adjacent sequences: A068759 A068760 A068761 * A068763 A068764 A068765
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KEYWORD
| easy,sign
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AUTHOR
| Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Feb 28 2002
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