21057

Appears in sequences

• Number of nonisomorphic ways a loop can cross three roads meeting in a Y n times (orbits under symmetry group of order 6).at n=14A078105
• Numbers k such that 6*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=24A098088
• Expansion of Product_{k>=1} 1/(1-x^(3*k-1))^k.at n=52A262876
• a(n) = A273059(4n+1).at n=25A275917