21890

Appears in sequences

• Length of n-th term in Look and Say sequences A005150 and A007651.at n=35A005341
• Number of recursive calls needed to compute the n-th Fibonacci number F(n), starting with F(1) = F(2) = 1.at n=20A019274
• a(n) = 2*Fibonacci(n+2) + ((-1)^n - 3)/2.at n=19A066629
• Starting at the chess position shown, a(n) is the number of ways Black can make n consecutive moves, followed by a checkmate in one move by White.at n=23A078993
• Partial sums of repeated Fibonacci sequence.at n=39A094707
• Diagonal sums of number triangle A132046.at n=20A154327
• a(n) = a(n-1)+ [least square > a(n-1)].at n=12A166068
• Length of the n-th term in the modified Look and Say sequence A110393.at n=37A179999
• Triangle of coefficients of polynomials u(n,x) jointly generated with A209136; see the Formula section.at n=50A209135
• a(0)=1, a(1)=-2; a(n+2) = a(n+1) + a(n) + (period 3: repeat 3, 1, -1).at n=22A226328
• Numbers m with C(2*m, m) + prime(m) prime, where C(2*m, m) = (2*m)!/(m!)^2.at n=50A236242
• Numbers n such that n^9+9 and n^9-9 are prime.at n=18A239505
• Partial sums of the number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 545", based on the 5-celled von Neumann neighborhood.at n=27A272836
• Partial sums of L(1) - F(1) + L(2) - F(2) + L(3) - F(3) + ..., where L = A000032 and F = A000045.at n=39A355019