20211021 has 12 divisors (see below), whose sum is σ = 29238300.
Its totient is φ = 13453440.
The previous prime is 20211007. The next prime is 20211031. The reversal of 20211021 is 12011202.
It can be written as a sum of positive squares in 2 ways, for example, as 11655396 + 8555625 = 3414^2 + 2925^2
It is not a de Polignac number, because 20211021 - 213 = 20202829 is a prime.
It is a Harshad number since it is a multiple of its sum of digits (9).
It is a Curzon number.
It is a junction number, because it is equal to n+sod(n) for n = 20210994 and 20211012.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (20211001) by changing a digit.
It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6655 + ... + 9203.
It is an arithmetic number, because the mean of its divisors is an integer number (2436525).
Almost surely, 220211021 is an apocalyptic number.
It is an amenable number.
20211021 is a deficient number, since it is larger than the sum of its proper divisors (9027279).
20211021 is a wasteful number, since it uses less digits than its factorization.
20211021 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 3436 (or 3433 counting only the distinct ones).
The product of its (nonzero) digits is 8, while the sum is 9.
The square root of 20211021 is about 4495.6669138182.
Note that the first 3 decimals coincide.
The cubic root of 20211021 is about 272.3930888296.
Adding to 20211021 its reverse (12011202), we get a palindrome (32222223).
The spelling of 20211021 in words is "twenty million, two hundred eleven thousand, twenty-one".