51271

Appears in sequences

• Nonprime numbers n such that phi(n) divides n^2 - 1, where phi(n) (A000010) is Euler's totient function.at n=20A098271
• Numerator of H(n+4) - H(n), where H(n) = Sum_{k=1..n} 1/k.at n=27A189642
• Number of (w,x,y,z) with all terms in {1,...,n} and 2*w*x>=3*y*z.at n=19A211923
• Composite squarefree numbers k such that k^2-1 is divisible by p-1 and p+1, where p are all the prime factors of k.at n=7A306685