19043

Appears in sequences

• a(n) = (4*n+1)*(4*n+3).at n=34A001539
• Products of 2 successive primes.at n=32A006094
• Numbers that are the product of a pair of twin primes.at n=10A037074
• Numbers n such that n^2 - 1 is expressible as the sum of two nonzero squares in exactly one way.at n=39A050797
• Inverse Mertens function: smallest k such that |M(k)| = n, where M(x) is Mertens's function A002321.at n=43A051402
• An inverse to Mertens's function: smallest k >= 2 such that Mertens's function |M(k)| (see A002321) is equal to n.at n=44A060434
• Smallest solution m to (n+1)*phi(m) = n*sigma(m), or -1 if no solution exists.at n=33A065824
• a(n) = A065824(A047845(n+1)).at n=15A065884
• Composite numbers k that divide Fibonacci(k+1).at n=9A069107
• Product of twin primes of form (4*k+1,4*k+3), k>0.at n=5A071697
• Multiplicative closure of twin prime pair products (A037074).at n=22A074480
• Odd Fibonacci pseudoprimes: odd composite numbers k such that either (1) k divides Fibonacci(k-1) if k == +-1 (mod 5) or (2) k divides Fibonacci(k+1) if k == +-2 (mod 5).at n=17A081264
• a(n) = A088314(n) - A000009(n).at n=49A088571
• a(n) = prime(2*n-1)*prime(2*n).at n=16A089581
• Numbers n such that n+1 and phi(n)+1 are both perfect squares.at n=19A089952
• Numbers k such that k+1 and sigma(k)+1 are both perfect squares.at n=14A089954
• Odd composites m that divide Fibonacci(m)-1.at n=10A094394
• Numbers k that divide Lucas(k) + 1.at n=34A094398
• Odd numbers k that divide Lucas(k) + 1.at n=12A094399
• Numbers k that divide both Fibonacci(k+1) and Lucas(k) + 1.at n=6A094402