381923

Appears in sequences

• Numbers that are the product of a pair of twin primes.at n=27A037074
• Product of twin primes of form (4*k+1,4*k+3), k>0.at n=13A071697
• Numbers k such that k+1 and sigma(k)+1 are both perfect squares.at n=36A089954
• Numbers that are one less than a square and have exactly 4 divisors.at n=28A134020
• Semiprimes k that divide Fibonacci(k+1).at n=34A177745
• Semiprimes which are sub-perfect powers.at n=41A189045
• Numbers k that form a primitive Pythagorean triple with k' and sqrt(k^2 + k'^2), where k' is the arithmetic derivative of k.at n=30A210503
• Smallest i such that prime(n) divides gcd(sigma(i), phi(i)) (cf. A009223).at n=26A222714
• Semiprimes p*q for which p and q are successive primes and their binary representations differ from each other in one bit position only.at n=29A261080
• Numbers k such that k^2 + sopfr(k)^2 is a square, where sopfr = A001414.at n=30A386991