

A186103


n such that n  sigma(n1)+sigma(n+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.
a(16) > 10^13.  Giovanni Resta, Apr 04 2014


LINKS

Table of n, a(n) for n=1..15.
J. M. Bergot, et al., How rare is 13?, sci.math discussion


EXAMPLE

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


MAPLE

with(numtheory): P:=proc(q) local n; for n from 2 to q do
if frac((sigma(n1)+sigma(n+1))/n)=0 then print(n); fi; od; end: P(10^9); # Paolo P. Lava, Nov 23 2017


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

Sequence in context: A044581 A126423 A072474 * A194713 A047638 A010929
Adjacent sequences: A186100 A186101 A186102 * A186104 A186105 A186106


KEYWORD

nonn,more


AUTHOR

J. M. Bergot, Feb 12 2011


EXTENSIONS

a(15) from Giovanni Resta, Apr 04 2014


STATUS

approved



