20491

Appears in sequences

• Number of unlabeled mappings (or mapping patterns) from n points to themselves; number of unlabeled endofunctions.at n=11A001372
• Strong pseudoprimes to base 55.at n=10A020281
• Numbers n for which there are exactly ten k such that n = k + reverse(k).at n=19A072434
• Composite numbers such that all divisors >1 have the same number of 1's in binary representation.at n=37A089042
• Number of length 3+1 0..n arrays with the sum of adjacent differences multiplied by some arrangement of +-1 equal to zero.at n=19A250168
• a(n) is the least integer k such that there are n values of i <= k for which gpf(i^2 + 1) = gpf(k^2 + 1), where gpf(x) is the greatest prime factor of x.at n=27A258840
• Numbers k of the form (x + y)*(x^2 + y^2) such that (x + y) and (x^2 + y^2) are primes.at n=32A349202