21020 has 12 divisors (see below), whose sum is σ = 44184.
Its totient is φ = 8400.
The previous prime is 21019. The next prime is 21023. The reversal of 21020 is 2012.
It is a Harshad number since it is a multiple of its sum of digits (5).
It is a junction number, because it is equal to n+sod(n) for n = 20995 and 21013.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (21023) by changing a digit.
It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 506 + ... + 545.
It is an arithmetic number, because the mean of its divisors is an integer number (3682).
221020 is an apocalyptic number.
21020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.
It is an amenable number.
21020 is an abundant number, since it is smaller than the sum of its proper divisors (23164).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22092).
21020 is a wasteful number, since it uses less digits than its factorization.
21020 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 1060 (or 1058 counting only the distinct ones).
The product of its (nonzero) digits is 4, while the sum is 5.
The square root of 21020 is about 144.9827575955.
The cubic root of 21020 is about 27.5979974743.
Adding to 21020 its reverse (2012), we get a palindrome (23032).
The spelling of 21020 in words is "twenty-one thousand, twenty", and thus it is an iban number.