21440

Appears in sequences

• Number of series-parallel networks with n edges.at n=12A001677
• Number of n-step self-avoiding walks on hexagonal lattice from (0,0) to (0,2).at n=8A003290
• Coordination sequence for 4-dimensional cubic lattice (points on surface of 4-dimensional cross-polytope).at n=20A008412
• Coordination sequence for C_4 lattice.at n=10A019560
• Reverse and add (in base 3).at n=15A035523
• Numbers that are divisible by 10 and are differences between two cubes in at least one way.at n=28A038854
• Numbers k such that k^2 + 1 is composite and phi(k^2 + 1) == 0 (mod k).at n=34A067519
• Number of 10-almost primes k such that 2^n < k <= 2^(n+1).at n=22A120041
• a(1)=1, a(n) = a(n-1) + n^3 if n odd, a(n) = a(n-1) + n^2 if n is even.at n=19A140154
• Triangle T(n, k) = ( k*(n-k+1) )^3 - 2^(n-1), read by rows.at n=48A141388
• Triangle T(n, k) = ( k*(n-k+1) )^3 - 2^(n-1), read by rows.at n=51A141388
• G.f. is the polynomial (1-x^3) * (1-x^6) * (1-x^9) * (1-x^12) * (1-x^15) * (1-x^18) / (1-x)^6.at n=24A162539
• G.f. is the polynomial (1-x^3) * (1-x^6) * (1-x^9) * (1-x^12) * (1-x^15) * (1-x^18) / (1-x)^6.at n=33A162539
• Triangle T(n,k) represents the coefficients of (x^16*d/dx)^n, where n=1,2,3,...; generalization of Stirling numbers of second kind A008277, Lah-numbers A008297.at n=18A223518
• G.f.: A(x) = 1 + x*B(x), where B(x) = 1 + x^2*C(x)^2, C(x) = 1 + x^3*D(x)^3, D(x) = 1 + x^4*E(x)^4, ...at n=36A228866
• Expansion of phi(x)^2 / phi(-x^2) in powers of x where phi() is a Ramanujan theta function.at n=33A260314
• Number of partitions of n where each part i is marked with a word of length i over a denary alphabet whose letters appear in alphabetical order.at n=4A261744
• G.f.: Sum_{n=-oo..+oo} (1 + x^n)^n / (1 - x^n)^n, ignoring the constant term.at n=56A292180
• Square array T(n,k), n >= 0, k >= 0, read by antidiagonals, where T(n,k) is the coefficient of x^(k*n) in expansion of ( (1 + x)/(1 - x) )^n.at n=49A336521
• Indices of the triangular numbers in A189475.at n=24A358417