20 Answers votes newest views recent 15Where is number theory used in the rest of mathematics? 13Not especially famous, long-open problems which anyone can understand 9Will quantum computing kill cryptography ? 3What are the major open problems in design theory nowaday? 3Quantum algorithms for dummies 2Difference of the maximum eigenvalue of a graph with the one of one-edge-deleted subgraph 2Ramsey numbers and graph spectra 2How might M.C. Escher have designed his patterns? 2Good programs for drawing graphs ( directed weighted graphs ) 2Interesting applications of the Pigeon-hole Principle 2The generator polynomial of cyclic code 1Generalizing Euclid’s proof of the infinity of primes 1practical applications of eigenvalues and eigenvectors 1Looking for a collection of entry level proofs 1Covering radius of LDPC codes 1Convergence of Eigenvalues 1Spectrum of a Laplacianized matrix 1Examples of interesting false proofs 1Is there any proof that you feel you do not “understand”? 0Does every bipartite graph with 512 edges have an induced subgraph with 256 edges?