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A067135
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Numbers k such that sigma(k+2) = 2*sigma(k-2).
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4
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5, 13, 313, 1153, 26206, 100318, 111928, 160873, 363283, 644278, 1676428, 2097808, 2639518, 3875998, 5349238, 5738773, 5903638, 6045583, 11272903, 13192933, 17242333, 18234403, 19667998, 29520643, 29595193, 31944238, 36918448, 37049803, 37201813, 43522288
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OFFSET
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1,1
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COMMENTS
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For each term given here except 5, k+2 is divisible by 3, but that's not always true: k=149784995358 is a counterexample. Also, k+2 is divisible by 5 for all terms here except 5 and 26206, but it is also not true for k=70333261.
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LINKS
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Vincenzo Librandi and Donovan Johnson, Table of n, a(n) for n = 1..500 (first 80 terms from Vincenzo Librandi)
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MAPLE
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with(numtheory); A067135:=proc(q) local n;
for n from 2 to q do if sigma(n+2)=2*sigma(n-2) then print(n); fi; od; end:
A067135 (10^10); # Paolo P. Lava, Apr 04 2013
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MATHEMATICA
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Do[If[DivisorSigma[1, n+2] == 2*DivisorSigma[1, n-2], Print[n]], {n, 2, 10^9}] (* Ryan Propper, Sep 26 2005 *)
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CROSSREFS
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Cf. A067134.
Sequence in context: A124878 A085554 A226664 * A122900 A145557 A012033
Adjacent sequences: A067132 A067133 A067134 * A067136 A067137 A067138
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KEYWORD
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nonn
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AUTHOR
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Benoit Cloitre, Feb 18 2002
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EXTENSIONS
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Edited by Dean Hickerson, Feb 20 2002
More terms from Ryan Propper, Sep 26 2005
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STATUS
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approved
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