21001921 has 8 divisors (see below), whose sum is σ = 22014720. Its totient is φ = 19997472.

The previous prime is 21001909. The next prime is 21001933. The reversal of 21001921 is 12910012.

It is an interprime number because it is at equal distance from previous prime (21001909) and next prime (21001933).

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

It is a cyclic number.

It is not a de Polignac number, because 21001921 - 2⁵ = 21001889 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21001895 and 21001904.

It is not an unprimeable number, because it can be changed into a prime (21001961) 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, 3400 + ... + 7318.

It is an arithmetic number, because the mean of its divisors is an integer number (2751840).

Almost surely, 2^21001921 is an apocalyptic number.

It is an amenable number.

21001921 is a deficient number, since it is larger than the sum of its proper divisors (1012799).

21001921 is a wasteful number, since it uses less digits than its factorization.

21001921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4175.

The product of its (nonzero) digits is 36, while the sum is 16.

The square root of 21001921 is about 4582.7852884463. The cubic root of 21001921 is about 275.9008299107.

Adding to 21001921 its reverse (12910012), we get a palindrome (33911933).

The spelling of 21001921 in words is "twenty-one million, one thousand, nine hundred twenty-one".