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A024816
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Antisigma(n): sum of numbers less than n which do not divide n.
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21
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0, 0, 2, 3, 9, 9, 20, 21, 32, 37, 54, 50, 77, 81, 96, 105, 135, 132, 170, 168, 199, 217, 252, 240, 294, 309, 338, 350, 405, 393, 464, 465, 513, 541, 582, 575, 665, 681, 724, 730, 819, 807, 902, 906, 957, 1009, 1080, 1052, 1168, 1182, 1254, 1280, 1377, 1365
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| a(n) is the sum of proper non-divisors of n. [From Omar E. Pol (info(AT)polprimos.com), May 25 2010]
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LINKS
| N. J. A. Sloane, Table of n, a(n) for n = 1..10000
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FORMULA
| a(n) = n*(n+1)/2 - sigma(n) = A000217-A000203.
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EXAMPLE
| a(12)=50 as 5+7+8+9+10+11 = 50 (1,2,3,4,6 not included as they divide 12)
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MATHEMATICA
| Table[n(n + 1)/2 - DivisorSigma[1, n], {n, 55}] (Robert G. Wilson v)
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CROSSREFS
| Cf. A023896, A066760.
Cf. A173539, A173540. Row sums of triangle A173541. [From Omar E. Pol (info(AT)polprimos.com), May 25 2010]
Sequence in context: A133066 A131988 A092593 * A196443 A007316 A163905
Adjacent sequences: A024813 A024814 A024815 * A024817 A024818 A024819
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KEYWORD
| easy,nonn,nice
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AUTHOR
| Paul Jobling (paul.jobling(AT)whitecross.com)
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