21487

Properties

Appears in sequences

• Largest prime == 7 (mod 8) with class number 2n+1.at n=20A002147
• Number of Twopins positions.at n=26A005691
• Second member of a sexy prime quadruple: value of p+6 such that p, p+6, p+12 and p+18 are all prime.at n=36A046122
• Fourth term of strong prime sextets: p(m-2)-p(m-3) > p(m-1)-p(m-2) > p(m)-p(m-1) > p(m+1)-p(m) > p(m+2)-p(m+1).at n=4A054816
• Initial term in sequence of four consecutive primes separated by 3 consecutive differences each <=6 (i.e., when d=2,4 or 6) and forming d-pattern=[4,2,6]; short d-string notation of pattern = [426].at n=11A078850
• Primes p such that the differences between the 5 consecutive primes starting with p are (4,2,6,4).at n=2A078953
• Primes p such that 6p + 1 and (p-1)/6 are primes.at n=35A085957
• Primes p such that p + 2^2, p + 4^2 and p + 6^2 are also primes.at n=33A092475
• Primes p such that p*floor(p/2)-2 and p*floor(p/2)+2 are also prime numbers.at n=25A164621
• Number of ordered triples (w,x,y) with all terms in {1,...,n} and w^3 >= x^3 + y^3.at n=42A211651
• Primes of the form 4k+3 generated recursively: a(1)=3, a(n)= Min{p; p is prime; Mod[p,4]=3; p|4Q^2-1}, where Q is the product of all previous terms in the sequence.at n=24A217759
• Primes of the form 6*p + 1 with p prime that are also of the form x^2 + 27*y^2 and congruent to 7 mod 24.at n=25A256172
• Primes of the form k!6-18, where k!6 is the sextuple factorial number (A085158).at n=2A289732
• Primes p such that the sum of 2^k for k such that 2^k < p and p+2^k is prime is greater than p.at n=47A345214
• Discriminants of imaginary quadratic fields with class number 41 (negated).at n=27A351679
• Primes p such that p + 4, p + 12 and p + 16 are also primes.at n=19A384298
• Prime numbersat n=2409