A prime circle of order
is a free circular permutation of the numbers
from 1 to
with adjacent pairs summing to a prime.
The number of prime circles for
, 2, ..., are 1, 1, 1, 2, 48, 512, ... (OEIS A051252).
The prime circles for the first few even orders are given in the table below.
| prime circles | |
| 2 | |
| 4 | |
| 6 | |
| 8 |