a_{1} \equal{}1, a_{n\plus{}1} \equal{}\frac{a_{n} }{\sqrt{1\plus{}4a_{n}^{2} } } for n≥1. What is the least k such that a_{k} <10^{\minus{}2} ?<spanclass=′latex−bold′>(A)</span> 2501<spanclass=′latex−bold′>(B)</span> 251<spanclass=′latex−bold′>(C)</span> 2499<spanclass=′latex−bold′>(D)</span> 249<spanclass=′latex−bold′>(E)</span> None quadraticsarithmetic sequence