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A067081 Numbers n such that sigma(n+1) = 2*sigma(n). 6
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sequence seems to consist only of odd values.

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..761

MAPLE

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

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 *)

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: A196425 A193612 A195949 * A195801 A154022 A013710

Adjacent sequences:  A067078 A067079 A067080 * A067082 A067083 A067084

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Feb 18 2002

EXTENSIONS

Terms added by Harry J. Smith, May 08 2010

STATUS

approved

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Last modified November 21 13:53 EST 2017. Contains 295001 sequences.