Novelty of a research paper Suppose I found out an algorithm/theorem, which is easy to understand and may be easy for the experts in the field to get it (with either same or different language). But after literature survey, If I strongly came to know that it is not yet published anywhere. Can I send my paper to the reputed journal for reviewing? 

In concise, my doubt is whether the novelty of a research paper refers to the novelty with respect to the existing literature or has to be completely new in that field such that hard to reach it.
The goal of a research paper is to advance the knowledge of the field. There is no goal that every known fact be documented in scientific literature. So, you need to ask yourself whether your work truly contributes to the body of knowledge. If unsure, ask a supervisor, colleague or the editor of the journal you would consider submitting to.

Besides advancing the state of knowledge there is also the question of whether the contribution is significant. If others can arrive at the same conclusion with minimal work, journals (especially more reputed ones) may reject your paper because it is not significant enough.