21521969 has 4 divisors (see below), whose sum is σ = 24596544. Its totient is φ = 18447396.

The previous prime is 21521963. The next prime is 21521971. The reversal of 21521969 is 96912512.

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 a de Polignac number, because none of the positive numbers 2^k-21521969 is a prime.

It is a super-2 number, since 2×21521969² = 926390299273922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21521963) 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, 1537277 + ... + 1537290.

It is an arithmetic number, because the mean of its divisors is an integer number (6149136).

Almost surely, 2^21521969 is an apocalyptic number.

It is an amenable number.

21521969 is a deficient number, since it is larger than the sum of its proper divisors (3074575).

21521969 is an equidigital number, since it uses as much as digits as its factorization.

21521969 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3074574.

The product of its digits is 9720, while the sum is 35.

The square root of 21521969 is about 4639.1776210876. The cubic root of 21521969 is about 278.1595662799.

The spelling of 21521969 in words is "twenty-one million, five hundred twenty-one thousand, nine hundred sixty-nine".