The minimum number of $$JK$$ flip-flops required to construct a synchronous counter with the count sequence $$\left( {0,0,1,1,2,2,3,3,0,0,...} \right)$$ is ____________.

A graph is self-complementary if it is isomorphic to its complement. For all self-complementary graphs on $$n$$ vertices, $$n$$ is

In a connected graph, bridge is an edge whose removal disconnects a graph. Which one of the following statements is true?

The number of onto functions (subjective functions) from set $$X = \left\{ {1,2,3,4} \right\}$$ to set $$Y = \left\{ {a,b,c} \right\}$$ is __________________.