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A157449
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Difference between n and the sum of its divisors except 1 and itself.
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2
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2, 3, 2, 5, 1, 7, 2, 6, 3, 11, -3, 13, 5, 7, 2, 17, -2, 19, -1, 11, 9, 23, -11, 20, 11, 15, 1, 29, -11, 31, 2, 19, 15, 23, -18, 37, 17, 23, -9, 41, -11, 43, 5, 13, 21, 47, -27, 42, 8, 31, 7, 53, -11, 39, -7, 35, 27, 59, -47, 61, 29, 23, 2
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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COMMENTS
| a(n) = n - k where k is the sum of the divisors of n excluding 1 and n itself. The initial value for n is 2.
Evidently a(n) = n iff n is prime (A000040). Moreover a(n) = 1 iff n is perfect (A000396).
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LINKS
| F. Guidi, Table of n, a(n) for n=2,...,100001
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EXAMPLE
| The divisors of 10 are 1, 2, 5 and 10, so a(10) = 10 - (2 + 5) = 3.
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CROSSREFS
| Cf. A000040, A000396.
Sequence in context: A098228 A081303 A164880 * A127705 A053139 A124386
Adjacent sequences: A157446 A157447 A157448 * A157450 A157451 A157452
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KEYWORD
| sign
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AUTHOR
| Ferruccio Guidi (fguidi(AT)cs.unibo.it), Mar 01 2009
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