21120

Appears in sequences

• Values of phi(k) when phi(k) = phi(k+1).at n=29A003275
• Area of more than one Pythagorean triangle.at n=19A009127
• a(n) = 2^n * (3n)! / (2n+1)!.at n=4A014298
• Expansion of (1+2x)/(1-2x)^4 (E.g.f.).at n=4A014484
• a(n) = Sum_{k=0..floor((n-1)/2)} T(n,k) * T(n,k+2), with T given by A026022.at n=7A027296
• Theta series of extremal 3-modular even lattice in dimension 20.at n=3A034620
• Composite numbers divisible by the palindromic sum of their prime factors (counted with multiplicity).at n=35A046358
• Composite numbers divisible by the palindromic sum of their palindromic prime factors (counted with multiplicity).at n=19A046366
• Expansion of (-1 + 1/(1-8*x)^8)/(64*x); related to A053107.at n=3A053111
• Triangle of coefficients of Chebyshev's U(n,2*x-1) polynomials (exponents of x in increasing order).at n=31A053124
• Triangle of coefficients of Chebyshev's U(n,2*x-1) polynomials (exponents of x in decreasing order).at n=32A053125
• Fifth column of Lanczos triangle A053125 (decreasing powers).at n=3A054323
• Numbers k such that sigma(k)+1 is a square and sets a new record for such squares.at n=38A063729
• Numbers that are palindromic in base 2 as well as in base 10 (initial zeros may be prepended).at n=43A069024
• Number of rooted unicursal planar maps with n edges and no vertices of valency 1 (unicursal means that exactly two vertices are of odd valency; there is an Eulerian path).at n=6A069721
• Product of all n - d, where d < n and d is a divisor of n.at n=32A072513
• Numbers k not in A065036 but such that tau(k) = omega(k)^3.at n=20A074853
• Numbers k such that Omega(k) = Omega(k+1) + Omega(k+2) + Omega(k+3) + Omega(k+4) where Omega(k) denotes the number of prime factors of k, counting multiplicity.at n=20A078094
• Numbers k such that Omega(k) = Omega(k-1) + Omega(k-2) + Omega(k-3) + Omega(k-4) where Omega(k) denotes the number of prime factors of k, counting multiplicity.at n=20A078095
• Sequence associated with recurrence a(n) = 2*a(n-1) + k*(k+2)*a(n-2).at n=7A080951