Humanity finally reach the value of 2021, and this time, as Mathematicians I would like to share some thoughts that have been found around the research paper, regarding the numbers that 2021 can be defined. What would be 2021 mean? How can this 2021 be unique from another value? Where is 2021? Which 2021 value can be describing us by the time or by the efficiency? These 4 chapters about 2021 become one of the basic ideas in Applied Mathematics that we can see, consider, and analyze further.