21563

Properties

Appears in sequences

• Third term of weak prime sextet: p(m-1)-p(m-2) < p(m)-p(m-1) < p(m+1)-p(m) < p(m+2)-p(m+1) < p(m+3)-p(m+2).at n=7A054830
• Primes of the form A108656(n-2)*n^2+A108656(n-1)*n+A108656(n).at n=43A108657
• Primes p that remain prime through at least 2 iterations of the function f(p) = p^2 + 4.at n=34A116886
• Primes congruent to 28 mod 59.at n=38A142755
• Supersafe primes.at n=36A181841
• Primes of the form k^2 + prime(k).at n=22A184935
• Numbers k such that (138^k + 137^k)/275 is prime.at n=7A227173
• Primes p such that p - d and p + d are also primes, where d is the largest digit of p.at n=18A245877
• Smallest of three consecutive primes in arithmetic progression with common difference 24 and digit sum prime.at n=29A253140
• Smallest prime that is the (sum, k*prime(k),k=m,..n+m-1) for some m, or 0 if no such m exists.at n=22A268467
• Primes p such that the base-10 concatenations (p+1)||p and (p+1)||(p+1)||p are both prime.at n=41A309749
• Discriminants of imaginary quadratic fields with class number 33 (negated).at n=33A351671
• a(0) = 1, a(n) = harmonic_mean(a(n-1), n), where harmonic_mean(p, q) = 2/(1/p + 1/q); denominators.at n=9A353251
• Prime numbersat n=2420