Haibike FullSeven 4 Electric Mountain Bike – 2021 – 52cm / Grey

2021 (MMXXI) was a common year starting on Friday of the Gregorian calendar, the 2021st year of the Common Era (CE) and Anno Domini (AD) designations, the 21st year of the 3rd millennium and the 21st century, and the 2nd year of the 2020s decade.

Like the year 2020, 2021 was also heavily defined by the COVID-19 pandemic, due to the emergence of multiple COVID-19 variants. The major global rollout of COVID-19 vaccines, which began at the end of 2020, continued in 2021. Most major events scheduled for 2020 that were postponed due to the pandemic were hosted in 2021, including the 26th United Nations Climate Change Conference, Expo 2020, and sporting events such as UEFA Euro 2020, the 2020 Summer Olympics and Paralympics, as well as the 2021 Copa América.

2021 additionally witnessed numerous advancements in space exploration, particularly by the United Arab Emirates, NASA and SpaceX, including the launch of the James Webb Space Telescope.

Civil unrest grew in 2021, with coups occurring in Sudan, Myanmar, Mali and Guinea, and insurrections occurring in Armenia and the United States.

4 (four) is a number, numeral and digit. It is the natural number following 3 and preceding 5.

4 is the smallest square number > 1, the smallest semiprime and composite number, and the 3rd highly composite number.

The number 4 is considered unlucky in many East Asian cultures.

Grey (more frequent British English) or gray (more frequent American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning that it has no chroma and therefore no hue. It is the color of a cloud-covered sky, of ash, and of lead.

The first recorded use of grey as a color name in the English language was in 700 CE. Grey is the dominant spelling in European and Commonwealth English, while gray is more common in American English; however, both spellings are valid in both varieties of English.

In Europe and North America, surveys show that gray is the color most commonly associated with neutrality, conformity, boredom, uncertainty, old age, indifference, and modesty. Only one percent of respondents chose it as their favorite color.

A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher than a hill, typically rising at least 300 metres (980 ft) above the surrounding land. A few mountains are isolated summits, but most occur in mountain ranges.

Mountains are formed through tectonic forces, erosion, or volcanism, which act on time scales of up to tens of millions of years. Once mountain building ceases, mountains are slowly leveled through the action of weathering, through slumping and other forms of mass wasting, as well as through erosion by rivers and glaciers.

High elevations on mountains produce colder climates than at sea level at similar latitude. These colder climates strongly affect the ecosystems of mountains: different elevations have different plants and animals. Because of the less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction, such as mining and logging, along with recreation, such as mountain climbing and skiing.

The highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is 8,850 m (29,035 ft) above mean sea level. The highest known mountain on any planet in the Solar System is Olympus Mons on Mars at 21,171 m (69,459 ft). The tallest mountain including submarine terrain is Mauna Kea in Hawaii from its underwater base at 9,330 m (30,610 ft) and some scientists consider it to be the tallest on earth.