21870021 has 8 divisors (see below), whose sum is σ = 29181664. Its totient is φ = 14569200.

The previous prime is 21870011. The next prime is 21870029. The reversal of 21870021 is 12007812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21870021 - 2⁵ = 21869989 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21870021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21870029) 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, 6246 + ... + 9096.

It is an arithmetic number, because the mean of its divisors is an integer number (3647708).

Almost surely, 2^21870021 is an apocalyptic number.

It is an amenable number.

21870021 is a deficient number, since it is larger than the sum of its proper divisors (7311643).

21870021 is a wasteful number, since it uses less digits than its factorization.

21870021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5411.

The product of its (nonzero) digits is 224, while the sum is 21.

The square root of 21870021 is about 4676.5394256865. The cubic root of 21870021 is about 279.6510150446.

Adding to 21870021 its reverse (12007812), we get a palindrome (33877833).

The spelling of 21870021 in words is "twenty-one million, eight hundred seventy thousand, twenty-one".