21557

Properties

Appears in sequences

• Numbers k such that 181*2^k-1 is prime.at n=44A050842
• First term of weak prime sextet: p(m+1)-p(m) < p(m+2)-p(m+1) < p(m+3)-p(m+2) < p(m+4)-p(m+3) < p(m+5)-p(m+4).at n=7A054828
• 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 pattern = [2, 4, 6]; short notation = [246] d-pattern.at n=26A078847
• Smallest member of a pair of consecutive twin prime pairs that have three primes between them.at n=30A089635
• Indices of primes in sequence defined by A(0) = 93, A(n) = 10*A(n-1) + 13 for n > 0.at n=8A101007
• Times in hours, minutes and seconds (to the nearest second) at which the hour and minute hands of an analog clock, if interchanged, continue to indicate some other albeit accurate times, over a complete 12-hour sweep for the slower hand. Leading zeros omitted.at n=27A121577
• Primes congruent to 22 mod 59.at n=38A142749
• Primes p such that the polynomial x^2 + x + p generates only primes for x = 1..6.at n=4A144051
• Primes p such that continued fraction of (1 + sqrt(p))/2 has period 7: primes in A146332.at n=33A146352
• Initial members of prime triples (p, p+2, p+6) for which also the sum 3p+8 is prime.at n=27A162001
• Numbers k such that k=prime(sigma(phi(pi(k)))).at n=6A163666
• Least prime p such that x^2+x+p produces primes for x=0..n-1 and composite for x=n.at n=7A164926
• Primes p such that (p, p+2, p+6, p+12) is a prime quadruple.at n=33A172454
• Primes q (except greater of twin primes) with result 2 under iterations of {r mod (max prime p < r)} starting at r = q.at n=25A175080
• Primes p such that the polynomial x^2 + x + p generates only primes for x = 0, ..., 4.at n=16A187057
• Primes p such that the polynomial x^2 + x + p generates only primes for x = 1..5.at n=7A187058
• Primes p such that the polynomial x^2 + x + p generates only primes for x = 1..7.at n=3A187060
• Initial primes of 5 consecutive primes with consecutive gaps 2, 4, 6, 8.at n=5A190814
• Initial primes of 6 consecutive primes with consecutive gaps 2,4,6,8,10.at n=1A190817
• Lexicographically earliest permutation of the primes such that successive absolute differences yield a permutation of all nonprime numbers.at n=40A203985