

A186103


Numbers k such that k  sigma(k1) + sigma(k+1).


3



13, 77, 489, 557, 1101, 1431, 2409, 8897, 538209, 2263024, 8910721, 13685781, 17428321, 962402769, 128508838576
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OFFSET

1,1


COMMENTS

The calculations were produced by V. Astanoff and Richard Tobin. Tobin has found that there are no other solutions up to 2*10^9.


LINKS



EXAMPLE

Take consecutive numbers 8896, 8897, 8898 to find that sigma(8896)=17780 and sigma(8898)=17808, with sum 35588=4*8897.


PROG

(PARI) sa=sigma(1); sb=sigma(2); for(n=2, 1e10, sc=sigma(n+1); if((sa+sc)%n==0, print1(n", ")); sa=sb; sb=sc) \\ Charles R Greathouse IV, Feb 13 2011


CROSSREFS



KEYWORD

nonn,more


AUTHOR



EXTENSIONS



STATUS

approved



