OFFSET
1,1
COMMENTS
Members of a pair (x,y) such that sigma(x) = sigma(y) = x + y - 1, where sigma = A000203.
The first time a pair ordered by its first element is not adjacent is x = 425500, y = 570405 which correspond to a(11) and a(13), respectively.
EXAMPLE
sigma(6160) = sigma(11697) = 6160 + 11697 - 1 = 17856.
MAPLE
with(numtheory): P:=proc(q) local a, b, n; for n from 1 to q do
a:=sigma(n)-n+1; b:=sigma(a)-a+1; if b=n and a<>b then print(n);
fi; od; end: P(10^9);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Apr 13 2017
STATUS
approved