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A067081
Numbers n such that sigma(n+1) = 2*sigma(n).
8
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
OFFSET
1,1
COMMENTS
Sequence seems to consist only of odd values.
LINKS
MATHEMATICA
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 *)
Position[Partition[DivisorSigma[1, Range[300000]], 2, 1], _?(2#[[1]]==#[[2]]&), 1, Heads->False]//Flatten (* Harvey P. Dale, Oct 21 2024 *)
PROG
(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
CROSSREFS
Sequence in context: A193612 A195949 A354654 * A195801 A154022 A013710
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 18 2002
EXTENSIONS
Terms added by Harry J. Smith, May 08 2010
STATUS
approved