21005020 has 24 divisors (see below), whose sum is σ = 44717904. Its totient is φ = 8286336.

The previous prime is 21005009. The next prime is 21005029. The reversal of 21005020 is 2050012.

21005020 = 500² + 501² + ... + 572².

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a junction number, because it is equal to n+sod(n) for n = 21004988 and 21005006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005029) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5734 + ... + 8653.

It is an arithmetic number, because the mean of its divisors is an integer number (1863246).

Almost surely, 2^21005020 is an apocalyptic number.

21005020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21005020 is an abundant number, since it is smaller than the sum of its proper divisors (23712884).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21005020 is a wasteful number, since it uses less digits than its factorization.

21005020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14469 (or 14467 counting only the distinct ones).

The product of its (nonzero) digits is 20, while the sum is 10.

The square root of 21005020 is about 4583.1233891310. The cubic root of 21005020 is about 275.9143996951.

Adding to 21005020 its reverse (2050012), we get a palindrome (23055032).

The spelling of 21005020 in words is "twenty-one million, five thousand, twenty".