20851

Appears in sequences

• Numbers n such that sigma(phi(n))/sigma(n) = 2.at n=33A067382
• a(n) = (9 + 14*n + 12*n^2 + 4*n^3)/3.at n=24A166911
• Numbers n such that n!3 + 3^10 is prime, where n!3 = n!!! is a triple factorial number (A007661).at n=27A261145
• a(n) = (prime(1+n)*prime(n)) + prime(n) + 1.at n=33A286624
• a(n) is the least number k such that the sum of n^2 consecutive primes starting at prime(k) is a square.at n=41A357813