18689

Appears in sequences

• Number of symmetric ways of folding a strip of n labeled stamps.at n=10A000560
• Odd nonprimes n such that n+d+1 is prime for all divisors d of n.at n=33A187554
• Number of 2Xn integer arrays with each element equal to the number of horizontal and antidiagonal neighbors exactly one smaller than itself.at n=9A266102
• Semiprimes p*q such that p*q+p+q, p*q-(p+q), p*q+2*(p+q) and p*q-2*(p+q) are all primes.at n=23A356765
• The internal state of the Sinclair ZX81 and Spectrum random number generator.at n=8A357907
• Composite numbers that contain only nonprime digits and whose prime factors contain only nonprime digits.at n=38A383934