20857

Properties

Appears in sequences

• Largest prime factor of 2^n + 1.at n=33A002587
• Largest primitive factor of 2^(2n+1) + 1.at n=16A002589
• Primes that divide at least one term of Sylvester's sequence s = A000058: s(n+1) = s(n)^2 - s(n) + 1, s(0) = 2.at n=35A007996
• Primes that are palindromic in base 11.at n=29A029978
• Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 26.at n=4A031614
• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 82 ones.at n=26A031850
• Denominators of continued fraction convergents to sqrt(416).at n=9A041791
• Number of asymmetric (identity) trees with n nodes and 4 leaves.at n=40A055335
• Diagonal sums of triangle A055249.at n=11A079282
• For p = prime(n), a(n) is the smallest prime q such that pq is a base-2 pseudoprime; that is, 2^(pq-1) = 1 mod pq; a(n) is 0 if no such prime exists.at n=17A085012
• List of primitive prime divisors of the Jacobsthal numbers A001045 in their order of occurrence.at n=35A129738
• Primes of the form 57x^2+18xy+193y^2.at n=36A140631
• Irregular triangle in which row n has all primes q such that prime(n)*q is a base-2 Fermat pseudoprime.at n=24A180471
• Positions of the incrementally largest terms in continued fraction for 2^(1/3).at n=9A181495
• Primes of the form 16n^2 + 121.at n=13A202083
• Number of cubic plane graphs with 2n nodes, minimal face size 3 and maximal face size 6.at n=29A219747
• Primes of form n^2 + 20736.at n=0A256840
• Largest prime factor of the n-th Jacobsthal number, A001045(n).at n=30A271314
• Largest prime factor of 8^n + 1.at n=11A274905
• Expansion of Sum_{i>=2} prime(i)*x^prime(i)/(1 - x^prime(i)) / Product_{j>=1} (1 - x^j).at n=25A281905