What is the next number in this sequence? (There are no hidden cubes.)
\[0, 1, 3, 6, 10, 15...\]
How many corners does a hypercube (a 4-dimensional cube) have?
How many line-segments are there in the 4th image of this growing tree sequence?
What is the sum of the first 13 positive odd numbers?
The sizes of the first 9 squares that make this spiral are:
\(1, 1, 2, 3, 5, 8, 13, 21, 34... \)
How big is the 10th square added to the spiral?