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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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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; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,100
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PROG
| (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
(PARI) u(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d)) { n=0; a=-1; for (m=1, 10^9, if(issquare(b=sigma(m) - u(m)), if(b>a, a=b; write("b063840.txt", n++, " ", m); if (n==100, break))) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Sep 01 2009]
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CROSSREFS
| Cf. A048146.
Sequence in context: A093648 A171221 A117101 * A180117 A167333 A045000
Adjacent sequences: A063837 A063838 A063839 * A063841 A063842 A063843
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KEYWORD
| nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Aug 25 2001
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