20389

Properties

Appears in sequences

• Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 18.at n=10A031606
• a(1) = 2, a(n) = k*a(n-1) + 1, where a(n) is the smallest prime of the form k*a(n-1) + 1 and k > 1.at n=7A059411
• Luhn primes: primes p such that p + (p reversed) is also a prime.at n=37A061783
• Class 7- primes.at n=6A081426
• Primes such that a sum of any two adjacent digits is prime; first and last digits are considered adjacent.at n=47A086244
• a(n) = n-th prime of Erdős-Selfridge classification n-.at n=6A101231
• Primes p such that p+1, p+2 and p+3 have equal number of divisors.at n=24A119711
• Primes congruent to 34 mod 59.at n=37A142761
• Primes congruent to 15 mod 61.at n=38A142813
• Primes p such that continued fraction of (1 + sqrt(p))/2 has period 7: primes in A146332.at n=32A146352
• Array t(n,k): row n consists of the positive integers m for which the least splitter of H(m) and H(m+1) is n, where H denotes harmonic number.at n=56A227631
• Primes of the form p(k)^2 + q(m)^2 with k > 0 and m > 0, where p(.) is the partition function (A000041), and q(.) is the strict partition function (A000009).at n=54A233346
• Number of partitions p of n not containing floor((min(p) + max(p))/2) as a part.at n=38A238483
• Consider two consecutive primes {p,q} such that P=2p+q and Q=2q+p are both prime. The sequence gives primes P.at n=41A248482
• Odd primes p for which there are exactly as many primes in the range [prevprime(p)^2, prevprime(p)*p] as there are in the range [prevprime(p)*p, p^2], where prevprime(p) gives the previous prime before prime p.at n=29A256473
• Number of n X 5 0..1 arrays with no element equal to more than one of its horizontal and vertical neighbors, with the exception of exactly two elements, and with new values introduced in order 0 sequentially upwards.at n=8A280551
• Numbers k such that (17*10^k - 41)/3 is prime.at n=19A291867
• a(n) = smallest prime q such that Sum_{primes p <= q} 1/sqrt(p) >= n.at n=37A292775
• Prime time primes on 6-digit clocks, second definition: primes of the form HMMSS where H, MM, SS are primes, H < 24, MM and SS < 60.at n=9A295013
• Primes p such that A001175(p) = (p-1)/6.at n=23A308791