21871

Properties

Appears in sequences

• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 100 ones.at n=11A031868
• Third term of weak prime sextet: p(m-1)-p(m-2) < p(m)-p(m-1) < p(m+1)-p(m) < p(m+2)-p(m+1) < p(m+3)-p(m+2).at n=8A054830
• Primes p such that the greatest prime divisor of p-1 is 5.at n=40A061599
• Primes of the form 10*3^k + 1.at n=4A068715
• Smallest prime larger than 3^n whose digits begin with those of 3^n.at n=7A068841
• Primes p such that p-1 and p+1 are both divisible by fourth powers.at n=13A086709
• Smallest prime of the form an n-th power followed by digit 1.at n=6A089318
• G.f.: x*(1 - x + x^2)/((1-x)^2 * (1 - x - x^2)).at n=19A104161
• Primes of the form 2^a * 3^b * 5^c + 1 for positive a, b, c.at n=31A114991
• Primes congruent to 41 mod 59.at n=38A142768
• Smallest of 3 consecutive prime numbers such that p1*p2*p3*d1*d2=average of twin prime pairs; p1,p2,p3 consecutive prime numbers; d1(delta)=p2-p1, d2(delta)=p3-p2.at n=19A153409
• a(n) = 729*n + 1.at n=29A158397
• a(n) = 30*n^2 + 1.at n=27A158558
• Gullwing primes: primes in the gullwing sequence A187220.at n=32A187222
• Start with 1 and 5, then repeatedly adjoin the smallest number that is greater than the last term and not equal to the sum of a subset of the existing terms.at n=18A188793
• Constant term of the reduction by x^2->x+1 of the polynomial p(n,x) defined below in Comments.at n=5A192460
• a(n) = 10*3^n+1.at n=7A199112
• Primes whose base-3 representation also is the base-2 representation of a prime.at n=35A235265
• A set of nine consecutive primes forming a 3 X 3 semimagic square with the smallest magic constant (65573).at n=6A265614
• Number of nX4 0..1 arrays with every element unequal to 0, 2, 3, 5 or 6 king-move adjacent elements, with upper left element zero.at n=8A304672