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A008885
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Aliquot sequence starting at 30.
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17
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30, 42, 54, 66, 78, 90, 144, 259, 45, 33, 15, 9, 4, 3, 1, 0
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OFFSET
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0,1
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COMMENTS
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The sum-of-divisor function A000203 and thus aliquot parts A001065 are defined only for positive integers, so the trajectory ends when 0 is reached, here at index 15. - M. F. Hasler, Feb 24 2018
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REFERENCES
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Richard K. Guy, Unsolved Problems in Number Theory, B6.
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LINKS
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FORMULA
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EXAMPLE
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a(0) = 30.
30 has eight divisors, 1, 2, 3, 5, 6, 10, 15, 30, which add up to 72, and 72 - 30 = 42, so a(1) = 42.
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MAPLE
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f := proc(n) option remember; if n = 0 then 30; else sigma(f(n-1))-f(n-1); fi; end:
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MATHEMATICA
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NestList[If[# > 0, DivisorSigma[1, #] - #, 0] &, 30, 80] (* Harvey P. Dale, Jun 12 2012 *)
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PROG
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(PARI) a(n, a=30)=for(i=1, n, a=sigma(a)-a); a \\ M. F. Hasler, Feb 24 2018
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CROSSREFS
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KEYWORD
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nonn,fini,full
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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