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Search: id:A063840
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| A063840 |
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Numbers n such that sigma(n) - usigma(n) is a square and sets a new record for such squares. |
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+0
1
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| 1, 18, 28, 40, 84, 120, 208, 372, 424, 552, 624, 900, 1152, 1848, 2784, 3904, 4488, 4992, 7448, 7896, 9120, 11712, 13720, 14280, 19920, 22344, 26040, 27144, 37920, 41160, 52920, 88920, 107100, 132480, 186732, 195300, 208152, 240240, 243432
(list; graph; listen)
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OFFSET
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1,2
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PROGRAM
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(PARI) a=-1; u(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d)); j=[]; for(n=1, 300000, x=sigma(n)-u(n); if(issquare(x), b=x; if(b>a, a=b; \ j=concat(j, n)))); j
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CROSSREFS
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Cf. A048146.
Adjacent sequences: A063837 A063838 A063839 this_sequence A063841 A063842 A063843
Sequence in context: A128858 A141782 A117101 this_sequence A045000 A032612 A092357
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KEYWORD
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nonn
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), Aug 25 2001
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