OFFSET
1,2
COMMENTS
Numbers k such that Sum_{j|k-1} (k mod j) + Sum_{j|k+1} (k mod j) is divisible by k.
a(6) > 10^8 if it exists.
EXAMPLE
MAPLE
filter:= proc(p) local d;
(numtheory:-tau(p-1) + numtheory:-sigma(p+1) - numtheory:-tau(p+1)-1) mod p = 0
end proc:
select(filter, [$1..10^5]);
CROSSREFS
KEYWORD
nonn,more
AUTHOR
J. M. Bergot and Robert Israel, May 25 2021
STATUS
approved