21404

Appears in sequences

• a(n) = 6*binomial(n,4) + 3*binomial(n,3) + 4*binomial(n,2) - n + 2.at n=17A066375
• Upper bound on number of regular triangulations of cyclic polytope C(n, n-4).at n=35A066456
• Least positive integer k such that prime(prime(k)), prime(prime(k*n)), prime(p) and prime(q) form a 4-term arithmetic progression for some pair of primes p and q.at n=6A261462
• Expansion of Product_{k>=1} (1 + x^(2*k-1))^(2*k-1).at n=29A262736
• Numbers k such that (268*10^k - 1)/3 is prime.at n=20A293531