130417

Appears in sequences

• G.f.: sqrt( Sum_{n>=0} x^n * Product_{k=1..n} (2*k - x) / (1 - 2*k*x) ).at n=6A231277
• E.g.f. satisfies log(A(x)) = x * (exp(x) - 1) * A(x)^3.at n=7A356798
• Odd numbers k > 1 such that gcd(5,k) = 1 and 5^((k-1)/2) == -(5/k) (mod k), where (5/k) is the Jacobi symbol (or Kronecker symbol); Euler pseudoprimes to base 5 (A262052) that are not Euler-Jacobi pseudoprimes to base 5 (A375914).at n=10A375816
• Centered hexagonal numbers that are sphenic numbers.at n=21A382628