27811

Appears in sequences

• 4-dimensional analog of centered polygonal numbers. Also number of regions created by sides and diagonals of a convex n-gon in general position.at n=30A006522
• a(n) is the number of subsets of {1,...,n} containing no solutions to x+y=z with x and y distinct (one version of "sum-free subsets").at n=21A085489
• 0 together with numbers k such that 8*R_k - 7 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=16A099421
• Expansion of (17-25*x-23*x^2+133*x^3)/(1-x)^4.at n=13A118587
• T(3n,2n), where T is the array in A047110.at n=4A127167
• Numbers k such that (85*10^k - 1)/3 is prime.at n=19A289942
• Number of regions in a polygon whose boundary consists of n+2 equally spaced points around the arc of a semicircle. See Comments for precise definition.at n=27A333643
• Triangle read by rows: T(n,k) is the number of connected graphs with n nodes and degeneracy k, 0 <= k < n.at n=38A352067