30673

Appears in sequences

• Strong pseudoprimes to base 43.at n=20A020269
• Binomial transform of A002024.at n=13A065979
• Number of different nonnegative solutions of equation: x^2 - y^2 = k! for 1 <= k <= n.at n=18A181893
• Centered 12-gonal numbers which are semiprimes, intersection of A003154 and A001358.at n=32A218172
• Euler pseudoprimes to base 5: composite integers such that abs(5^((n - 1)/2)) == 1 mod n.at n=22A262052
• a(n) = minimal value of n+k+1 such that the concatenation of the binary expansions of n,n+1,...,n+k is divisible by n+k+1, or -1 if no such n+k+1 exists.at n=32A332586
• a(n) = Sum_{1 <= i, j, k, l <= n} gcd(i,j,k,l).at n=12A344523
• G.f. A(x) satisfies: A(x) = x^2 + x^3 * exp(A(x) - A(x^2)/2 + A(x^3)/3 - A(x^4)/4 + ...).at n=36A346032
• Numbers k of the form (x + y)*(x^2 + y^2) such that (x + y) and (x^2 + y^2) are primes.at n=38A349202
• Numbers k such that gcd(2*k^7+1, 3*k^3+2) > 1.at n=26A369153
• 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=4A375816
• E.g.f. A(x) satisfies A(x) = exp(-x) + x*A(x)^3.at n=6A379878