# Find a square square pyramidal number

### Problem statement

Find a square square pyramidal number.

### Solution to metapuzzle: show

### Restated puzzle: show

Find a number which which is both square and square pyramidal.

### Solution to puzzle: show

Apart from 0 and 1, which may be considred trivial, the only solution is **4900**, which is the sum of the
first 24 positive squares. (This solution is asserted here on proofwiki
to be unique, without a proof.)

### Comments: show

I hope the metapuzzle is not too hard. The solution can be found by an obvious but tedious search.

I was surprised to find that this is a well-documented puzzle, known as the cannonball problem; and that its solution is related to the Leech lattice.

This is one of several pages on puzzles and metapuzzles.