February 19–February 25, 2008
Problem
This is a two-part problem this week. The first part is a warmup for the second.
- Show that if n is a triangular number, then so is 9n + 1. (Triangular numbers are 1, 3, 6, 10, ..., k(k+1)/2, ...)
- Find other numbers a and b so that an + b is triangular whenever n is.
Solution
here.
List of solvers
Dan Siddoway, Mark Bun, Steve Wilmarth (undergrad), Dustin Moody, Gary Raymond, Aneesh Hariharan (grad), Steven Gillispie (staff), Marina Meila (faculty), Rich Bauer (alum), Mike Goodman, Eric Brodeur, Lloyd Sakazaki (outside).
The winner this week is Dan Siddoway!