21288961 has 4 divisors (see below), whose sum is σ = 22214592. Its totient is φ = 20363332.

The previous prime is 21288959. The next prime is 21288973. The reversal of 21288961 is 16988212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21288961 - 2¹ = 21288959 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 21288961.

It is not an unprimeable number, because it can be changed into a prime (21288901) 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, 462781 + ... + 462826.

It is an arithmetic number, because the mean of its divisors is an integer number (5553648).

Almost surely, 2^21288961 is an apocalyptic number.

It is an amenable number.

21288961 is a deficient number, since it is larger than the sum of its proper divisors (925631).

21288961 is an equidigital number, since it uses as much as digits as its factorization.

21288961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 925630.

The product of its digits is 13824, while the sum is 37.

The square root of 21288961 is about 4613.9962071939. The cubic root of 21288961 is about 277.1520884095.

The spelling of 21288961 in words is "twenty-one million, two hundred eighty-eight thousand, nine hundred sixty-one".