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A067081
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Numbers n such that sigma(n+1) = 2*sigma(n).
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6
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5, 125, 1253, 1673, 3127, 5191, 7615, 12035, 43817, 47795, 48559, 49955, 56975, 58373, 61721, 63545, 68033, 78395, 97411, 106001, 108473, 109939, 111451, 111683, 123497, 123797, 131659, 137081, 192065, 192279, 224561, 228377, 274273, 280313
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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Sequence seems to consist only of odd values.
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LINKS
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Harry J. Smith, Table of n, a(n) for n = 1..761
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MAPLE
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A067081:=proc(q) local n;
for n from 1 to q do if sigma(n+1)=2*sigma(n) then print(n); fi; od; end:
A067081(10^10); # Paolo P. Lava, Mar 25 2013
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MATHEMATICA
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f[n_]:=DivisorSigma[1, n]; lst={}; Do[If[2*f[n]==f[n+1], AppendTo[lst, n]], {n, 9!}]; lst (* Vladimir Joseph Stephan Orlovsky, Jul 22 2009 *)
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PROG
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(PARI) { n=0; for (m=1, 10^10, if (sigma(m+1) == 2*sigma(m), write("b067081.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, May 08 2010
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CROSSREFS
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Sequence in context: A196425 A193612 A195949 * A195801 A154022 A013710
Adjacent sequences: A067078 A067079 A067080 * A067082 A067083 A067084
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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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Terms added by Harry J. Smith, May 08 2010
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STATUS
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approved
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