2021 is semi-prime because it has exactly 2 prime factors: 2021 = 43*47. It is also called a "brilliant" number because it is a semi-prime whose two prime factors have the same number of digits. The next brilliant year will be 2047.
2021 is deficient because the sum of its proper divisors (1 + 43 + 47 = 91) is less than 2021
2021 is the concatenation of two consecutive integers (20 and 21) and it is the product of two consecutive primes (43 and 47). The next such number is 2307340946901148 2307340946901147.
2021 is an "iban" number because when you write it out in English, you don't need the letter "i".
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