OFFSET
1,1
COMMENTS
a(5) > 10^13. - Giovanni Resta, Mar 13 2014
a(5) > 5*10^13. - Hiroaki Yamanouchi, Aug 27 2015
EXAMPLE
16' = 32, 17' = 1 and 16 + 17 = 32 + 1 = 33.
108' = 216, 109' = 1 and 108 + 109 = 216 + 1 = 217.
3294172' = 6588344, 3274173' = 1 and 3294172 + 3294173 = 6588344 + 1 = 6588345.
7975979' = 941063, 7975980' = 15010896 and 7975979 + 7975980 = 941063 + 15010896 = 15951959.
MAPLE
with(numtheory); P:= proc(q) local a, b, n, p; for n from 1 to q do
a:=n*add(op(2, p)/op(1, p), p=ifactors(n)[2]);
b:=(n+1)*add(op(2, p)/op(1, p), p=ifactors(n+1)[2]);
if 2*n+1=a+b then print(n); fi; od; end: P(10^9);
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Paolo P. Lava, Feb 19 2014
STATUS
approved