20921

Properties

Appears in sequences

• Numbers k such that the continued fraction for sqrt(k) has period 87.at n=14A020426
• Numbers whose base-12 representation has exactly 5 runs.at n=26A043654
• Prime number spiral (clockwise, Southwest spoke).at n=24A054568
• Primes p for which the period of reciprocal = (p-1)/8.at n=33A056213
• a(1) = 1, a(n) = prime equal to n-th partial sum of A073852.at n=12A073854
• Number of odious primes (A027697) in range ]2^n,2^(n+1)].at n=18A095005
• Let p(k) = k-th prime; sequence gives primes q of the form q = k*p(k) - 1 for some k.at n=7A096065
• Lesser prime in pair prime(k) +/- k for some k.at n=31A107636
• Odd primes generated recursively: a(1) = 3, a(n) = Min {p is prime; p divides Q+2}, where Q is the product of previous terms in the sequence.at n=22A125045
• Primes of the form 13*n^2+3*n+1.at n=19A176783
• Fourth 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=23A238676
• Hyperartiads.at n=18A270798
• Primes p whose reverse q is a semiprime, and of p+q and its reverse one is a prime and the other is a semiprime.at n=16A350781
• Primes whose position in the Wythoff array is immediately followed by a prime both in the next column and the next row.at n=10A352537
• Primes that contain at least two different even digits and at least two different odd digits such that any permutation of the odd digits and any permutation of the even digits produces a prime. Permutations with leading 0's are disregarded; i.e., if permutations of even digits in a prime p produce a number with a leading 0 that is not prime, p is still in the sequence.at n=31A377564
• Prime numbersat n=2353