21520351 has 4 divisors (see below), whose sum is σ = 22786272. Its totient is φ = 20254432.

The previous prime is 21520307. The next prime is 21520361. The reversal of 21520351 is 15302512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21520351 - 2²³ = 13131743 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520361) 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, 632935 + ... + 632968.

It is an arithmetic number, because the mean of its divisors is an integer number (5696568).

Almost surely, 2^21520351 is an apocalyptic number.

21520351 is a deficient number, since it is larger than the sum of its proper divisors (1265921).

21520351 is a wasteful number, since it uses less digits than its factorization.

21520351 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1265920.

The product of its (nonzero) digits is 300, while the sum is 19.

The square root of 21520351 is about 4639.0032334544. The cubic root of 21520351 is about 278.1525955197.

Adding to 21520351 its reverse (15302512), we get a palindrome (36822863).

The spelling of 21520351 in words is "twenty-one million, five hundred twenty thousand, three hundred fifty-one".