Enter a prime number in the box above to see if it appears in a Cunningham chain of length 2 or greater.
A Cunningham chain consists of prime numbers such that for each prime p, except the last, 2p + 1 is also prime (and is thus a Sophie Germain prime). Or, for each prime p, except the first, (p − 1)/2 is also prime (and is thus a safe prime). A prime that is neither a Sophie Germain prime nor a safe prime trivially forms a Cunningham chain of length 1.
Try the locator on a few primes listed in A156658 of N. J. A. Sloane's On-Line Encyclopedia of Integer Sequences.
NOTE: The locator is limited by the capabilities of JavaScript. A chain may display incomplete if any of its members are beyond what JavaScript can handle with integer precision. There is no mechanism to warn you if that happens. Also, moderately large numbers may cause your browser to slow down. In my testing with Firefox 59, the locator could handle inputs as large as 2147483647 without any problem. Any prime greater than that could cause sluggishness and/or incorrect results.