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A067135 Numbers k such that sigma(k+2) = 2*sigma(k-2). 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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.

LINKS

Vincenzo Librandi and Donovan Johnson, Table of n, a(n) for n = 1..500 (first 80 terms from Vincenzo Librandi)

MAPLE

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

MATHEMATICA

Do[If[DivisorSigma[1, n+2] == 2*DivisorSigma[1, n-2], Print[n]], {n, 2, 10^9}] (* Ryan Propper, Sep 26 2005 *)

CROSSREFS

Cf. A067134.

Sequence in context: A124878 A085554 A226664 * A122900 A145557 A012033

Adjacent sequences:  A067132 A067133 A067134 * A067136 A067137 A067138

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Feb 18 2002

EXTENSIONS

Edited by Dean Hickerson, Feb 20 2002

More terms from Ryan Propper, Sep 26 2005

STATUS

approved

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Last modified August 12 13:59 EDT 2022. Contains 356077 sequences. (Running on oeis4.)