21845

Appears in sequences

• a(2n) = 2*a(2n-1), a(2n+1) = 2*a(2n)+1 (also a(n) is the n-th number without consecutive equal binary digits).at n=15A000975
• Jacobsthal sequence (or Jacobsthal numbers): a(n) = a(n-1) + 2*a(n-2), with a(0) = 0, a(1) = 1; also a(n) = nearest integer to 2^n/3.at n=16A001045
• Sierpiński's triangle (Pascal's triangle mod 2) converted to decimal.at n=14A001317
• a(n) = (4^n - 1)/3.at n=8A002450
• Divisors of 2^16 - 1.at n=14A003527
• Divisors of 2^32 - 1 (for a(1) to a(31), the 31 regular polygons with an odd number of sides constructible with ruler and compass).at n=14A004729
• Indices of last windows of trapezoidal maps.at n=15A007873
• Triangle of central factorial numbers T(2*n,2*n-2*k), k >= 0, n >= 1 (in Riordan's notation).at n=43A008957
• Quadruples of different integers from [ 2,n ] with no common factors between triples.at n=31A015629
• Triangle of Gaussian binomial coefficients [ n,k ] for q = 4.at n=37A022168
• Gaussian binomial coefficients [ n,7 ] for q = 4.at n=1A022206
• a(n) = C(n,0) + C(n,3) + ... + C(n,3[n/3]).at n=16A024493
• a(n) = C(n,1) + C(n,4) + ... + C(n, 3*floor(n/3) + 1).at n=15A024494
• a(n) = Sum_{k=0..floor(n/2)} A026637(n, k).at n=15A026645
• Sum of n-th powers of divisors of 128.at n=2A034674
• Triangle read by rows: T(n,k) = T(n-1,k-1) + k^2*T(n-1,k), 1 < k <= n, T(n,1) = 1.at n=37A036969
• One-dimensional cellular automaton 'sigma-minus' (Rule 90): 000,001,010,011,100,101,110,111 -> 0,1,0,1,1,0,1,0.at n=7A038183
• Numbers n such that number of runs in the base 4 representation of n is congruent to 1 mod 8.at n=21A043851
• Numbers n such that number of runs in the base 4 representation of n is congruent to 1 mod 9.at n=21A043859
• Numbers n such that number of runs in the base 4 representation of n is congruent to 1 mod 10.at n=21A043868