21587

Properties

Appears in sequences

• Primes that remain prime through 3 iterations of function f(x) = 2x + 3.at n=32A023273
• Start of a string of exactly 3 consecutive (but disjoint) pairs of twin primes.at n=7A035791
• Number of partitions satisfying cn(2,5) + cn(3,5) <= cn(0,5) + cn(1,5) and cn(2,5) + cn(3,5) <= cn(0,5) + cn(4,5).at n=43A039865
• Numerators of continued fraction convergents to sqrt(180).at n=6A041332
• Sixth term of weak prime sextet: p(m-4)-p(m-5) < 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=7A054833
• Lesser of the first pair of three successive prime pairs (no isolated primes occur in between). Least of the six successive primes which are member of prime pairs.at n=10A090953
• A variation on Flavius's sieves (A000960, A099207): Start with the Chen primes; at the k-th sieving step, remove every (k+1)-st term of the sequence remaining after the (k-1)-st sieving step; iterate.at n=38A118500
• Lesser of twin primes (p,q=p+2) such that p*q-p-q and p*q+p+q are primes.at n=4A126334
• Primes p such that p*q-p-q and p*q+p+q are prime where q=nextprime(p).at n=40A128548
• First of six consecutive primes that are three sets of twin primes.at n=9A136143
• Total number of parts of multiplicity 6 in all partitions of n.at n=43A222706
• Number of compositions of n with exactly 8 transitions between different parts.at n=6A244720
• Initial members of prime quadruples (n, n+2, n+24, n+26).at n=21A245568
• Initial members of prime sextuples (p, p+2, p+12, p+14, p+24, p+26).at n=4A253624
• If n is 0, 1, or prime, a(n) = n; else a(n) = a(n-1) + a(n-2).at n=40A265822
• Primes that can be generated by the concatenation in base 4, in descending order, of two consecutive integers read in base 10.at n=14A287303
• Solution of the complementary equation a(n) = a(n-1) + a(n-2) + 2*b(n-1) + 2*b(n-2), where a(0) = 1, a(1) = 3, b(0) = 2, b(1) = 4.at n=15A294419
• Discriminants of imaginary quadratic fields with class number 37 (negated).at n=19A351675
• Number of integer partitions of n having a part that can be written as a nonnegative linear combination of the other (possibly equal) parts.at n=37A364913
• First of four consecutive primes with product p and sum s such that |s^2-p| and s^2+p are both prime.at n=17A391121