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
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.
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
J. M. Bergot, Feb 12 2011
EXTENSIONS
a(15) from Giovanni Resta, Apr 04 2014
STATUS
approved