Date: Wed, 9 Apr 1997 17:49:27 -0400
From: Alexander Bogomolny
The series consists of
one 1, two 2s, three 3s, ...
The sum of all numbers from 1 through n equals Sn = n(n+1)/2. You are looking for an n such that Sn < 1000000 but Sn+1 > 1000000. This number is 1413.
How do you get it? n*(n+1) < (n+1)2 < 2000000.
sqrt(2000000) is approximately 1414.2... So n+1=1414.
Regards
71529741