21491

Properties

Appears in sequences

• Primes that remain prime through 2 iterations of function f(x) = 8x + 1.at n=39A023260
• Let (p1,p2), (p3,p4) be pairs of twin primes with p1*p2=p3+p4-1; sequence gives values of p1.at n=22A047976
• Fifth term of strong prime sextets: p(m-3)-p(m-4) > p(m-2)-p(m-3) > p(m-1)-p(m-2) > p(m)-p(m-1) > p(m+1)-p(m).at n=4A054817
• Initial term in sequence of four consecutive primes separated by 3 consecutive differences each <=6 (i.e., when d=2,4 or 6) and forming d-pattern=[2,6,4]; short d-string notation of pattern = [264].at n=25A078848
• Smallest member of a pair of consecutive twin prime pairs that have three primes between them.at n=29A089635
• Smallest prime factor of prime(n)! / prime(n)# + 1.at n=39A103891
• Consider primes p such that integer part of the volume of cube with faces of area p is prime; sequence gives integer part of volumes.at n=14A107989
• a(n) = (n^3)/2 + (3*n^2)/2 + 3*n + 3.at n=33A127873
• Prime numbers of the form (x^3)/2+(3x^2)/2+3x+3.at n=11A127874
• Primes congruent to 15 mod 59.at n=38A142742
• Primes congruent to 19 mod 61.at n=39A142817
• Primes such that applying "reverse and add" twice produces two more primes.at n=2A174402
• Lesser of twin primes p1 such that p1*p2+-6 are prime numbers.at n=9A174955
• Lesser of twin primes p1 such that p1*p2-4 and p1*p2-6 are twin prime numbers.at n=13A174957
• Numbers k such that (19^k - 4^k)/15 is prime.at n=9A228076
• Primes p such that p+2, p+8, and p+12 are all prime.at n=32A233540
• Sixth prime p such that (p+n)^2+n is prime but (p+j)^2+j is not prime for all 0<j<n.at n=23A238678
• Positive k such that Lucas(3*k) - Fibonacci(k) is a prime.at n=13A245801
• a(n) = 2^n*(n/8 + 1) - n.at n=11A291097
• a(n) is the smallest lesser twin prime p from A001359 such that the distance to the previous lesser twin prime is 6*n.at n=18A340573