55779

Appears in sequences

• a(n) is the number of different graphs drawn in the following way: you decide for each number k <= n on a pair of positive numbers (x(k),y(k)) such that x(k)+y(k)=k; you draw n points numbered 1 to n; draw two arrows from n, one to x(n) and one to y(n); draw two arrows from each k already reached by an arrow, one to x(k) and one to y(k). The process stops when 1 is the only point reached by an arrow without any arrow leaving it; you can also erase the isolated points.at n=18A058050
• Numbers of the form x^2 + y^2 + z^2 = phi(x*y*z) + sigma(x*y*z).at n=40A173792
• Squarefree numbers differing by more than 3 from any other squarefree number.at n=4A268332
• T(i, j) = k is the least squarefree number with a run of exactly i>=0 nonsquarefree numbers immediately preceding k and a run of exactly j>=0 nonsquarefree numbers immediately succeeding k.at n=31A270996
• Number of unlabeled directed graphs on n nodes without a subgraph isomorphic to directed K_{2,2} that have the maximal number of edges (=A191873(n)).at n=10A351335
• a(n) is the least semiprime > a(n-2) + a(n-1), with a(1) = 4 and a(2) = 6.at n=19A366217