Problem Statement

A Cullen number is a number of the form n × 2n + 1 where n is a natural number. A Woodall number is very similar. It is a number of the form n × 2n - 1 where n is a natural number. So for each n the associated Cullen number and Woodall number differ by 2. Woodall numbers are sometimes referred to as Riesel numbers or Cullen numbers of the second kind.

Cullen primes are Cullen numbers that are prime. Similarly, Woodall primes are Woodall numbers that are prime. It is common to list the Cullen and Woodall primes by the value of n rather than the full evaluated expression. They tend to get very large very quickly. For example, the third Cullen prime, n == 4713, has 1423 digits when evaluated.

Let's start with the solution:

  [ dup << 1+ ]  is cullen  ( n --> n )

  [ dup << 1 - ] is woodall ( n --> n )

  say "First 20 Cullen numbers:" cr
  20 times [ i^ 1+ cullen echo sp ] cr
  cr
  say "First 20 Woodall numbers:" cr
  20 times [ i^ 1+ woodall echo sp ] cr