206981

Appears in sequences

• Strong pseudoprimes to base 31.at n=26A020257
• Euler transform of Thue-Morse sequence A001285.at n=34A029877
• Octagonal numbers (A000567) that are semiprimes (A001358).at n=25A259677
• a(n) is the smallest k such that the p-rank of (Z/kZ)* is 2, where p = prime(n) and (Z/kZ)* is the multiplicative group of integers modulo n.at n=31A307434
• Odd numbers k > 1 such that gcd(3,k) = 1 and 3^((k-1)/2) == -(3/k) (mod k), where (3/k) is the Jacobi symbol (or Kronecker symbol); Euler pseudoprimes to base 3 (A262051) that are not Euler-Jacobi pseudoprimes to base 3 (A048950).at n=9A375490