21084021 has 12 divisors (see below), whose sum is σ = 34805472. Its totient is φ = 12047976.

The previous prime is 21083989. The next prime is 21084047. The reversal of 21084021 is 12048012.

It is not a de Polignac number, because 21084021 - 2⁵ = 21083989 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21083985 and 21084003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21084521) 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, 167271 + ... + 167396.

It is an arithmetic number, because the mean of its divisors is an integer number (2900456).

Almost surely, 2^21084021 is an apocalyptic number.

21084021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21084021 is a deficient number, since it is larger than the sum of its proper divisors (13721451).

21084021 is a wasteful number, since it uses less digits than its factorization.

21084021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 334680 (or 334677 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 21084021 is about 4591.7339861974. The cubic root of 21084021 is about 276.2598765263.

The spelling of 21084021 in words is "twenty-one million, eighty-four thousand, twenty-one".