18287

Properties

Appears in sequences

• a(n) = smallest number with shortest addition chain of length n.at n=19A003064
• Primes p such that there is no Carmichael number pqr, p<q<r q, r primes.at n=21A051663
• Fifth term of weak prime quintets: p(m-3)-p(m-4) < p(m-2)-p(m-3) < p(m-1)-p(m-2) < p(m)-p(m-1).at n=44A054827
• Numbers n such that h(n) = 3 h(n-1) where h(n) is the length of the sequence {n, f(n), f(f(n)), ...., 1} in the Collatz (or 3x + 1) problem. (The earliest "1" is meant.)at n=12A078420
• Indices n such that the 3 X 3 matrix with components (row by row) prime(n+k), 0 <= k <= 8, has zero determinant.at n=25A117345
• Lesser of twin primes isolated from neighboring primes by +- 10 (or more).at n=36A138063
• Primes congruent to 56 mod 59.at n=40A142783
• Primes congruent to 48 mod 61.at n=34A142846
• Odd primes which can never divide 2^a+2^b+1.at n=30A179113
• Primes p such that x^41 = 2 has a solution mod p, and p is congruent to 1 mod 41.at n=1A190758
• Number of ordered triples (w,x,y) with all terms in {-n,...-1,1,...,n} and 2w+x+y>2.at n=17A211619
• The number of symmetric positive definite 2 X 2 matrices whose entries are integers of absolute value at most n.at n=26A219693
• a(n) = smallest prime q > a(n-1) such that 2*prime(n)*q^prime(n)+1 is also prime.at n=11A225747
• Primes p with p + 2 and prime(p) + 2 both prime.at n=38A236458
• Initial members of prime quadruples (n, n+2, n+24, n+26).at n=19A245568
• Numbers with largest ratio A003313(k)/log_2(k) in the range 2^n < k < 2^(n+1).at n=13A264803
• Odd primes p such that phi(p+1) = phi(phi(p-2)+1).at n=9A271656
• Smallest prime factor of A077586(n).at n=11A309130
• Primes with record values of corresponding Fortunate numbers (A005235).at n=42A317479
• Primes that do not divide any 3-Carmichael numbers.at n=18A369777