21906

Appears in sequences

• Coordination sequence for C_3 lattice: a(n) = 16*n^2 + 2 (n>0), a(0)=1.at n=37A010006
• Numbers k such that k!!!!!! - 1 is prime.at n=18A051592
• Numbers k such that (k / sum of digits of k) and (k+1 / sum of digits of k+1) are both prime.at n=22A085775
• Numbers n for which 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.at n=17A096846
• a(n) = least m such that sum of m reciprocal primes starting with n-th prime is >1.at n=23A137368
• Number of (w,x,y,z) with all terms in {1,...,n} and w < (geometric mean of x,y,z).at n=15A212141
• G.f. satisfies: A(x) = A(x/A(x))^2 - x.at n=7A241000
• Length of n-th iterate of the mapping 00->0010, 01->010, 10->000, starting with 00.at n=16A289019
• Numbers of the form k^2 + 2 that are the sums of two squares.at n=15A329170
• a(0)=0; for n > 0, a(n) = 2*a(n-1) if n-1 is prime, a(n-1) + 1 otherwise.at n=42A354973
• Numbers whose square and cube taken together contain each decimal digit at least twice.at n=3A363909