Update (2005-12-09): I recently learned that Mark Owen (aka Quinapalus) has a website where this puzzle, Interstice, can be found, along with many other novel creations. Highly recommended.

It is better to view his original version as I changed minor presentation details when I recorded it in my notes long ago. I'll keep this page around as a souvenir of one of the few times I've written nontrivial JavaScript code.

# Interstice by Quinapalus

 required for validator

p<q<r are three-digit primes, fixed throughout. All answer are to be written in base 10, unless otherwise stated.

Across
0 pqr
8 Sum of two squares, in base 8
9
11 2 x 13A
12 Multiple of p
13
14 Multiple of r
15 Prime, written in base 8
16 p + q + r
20
22
23 3D / 8
24
25 24A2 + 2
26 Square
28 Multiple of 81
29 3 x 0D - 2
Down
0
1 2 x 19D
2 19D / 2
3
4 3√20A + √9A
5
6 2 x 17D
7 2pqr
10 (Power of 2) + p
12
17 Square
18 1D + 2D
19
21
27 Composite

From "Eureka", the journal of the Cambridge University Mathematical Society.

Long ago, Dr. David Paget sent me this puzzle. I have yet to encounter a number puzzle that is as satisfying to solve as this one.