21511157 has 4 divisors (see below), whose sum is σ = 21595116. Its totient is φ = 21427200.

The previous prime is 21511153. The next prime is 21511159. The reversal of 21511157 is 75111512.

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

It can be written as a sum of positive squares in 2 ways, for example, as 9991921 + 11519236 = 3161^2 + 3394^2 .

It is a cyclic number.

It is not a de Polignac number, because 21511157 - 2² = 21511153 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 (21511151) 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, 41594 + ... + 42107.

It is an arithmetic number, because the mean of its divisors is an integer number (5398779).

Almost surely, 2^21511157 is an apocalyptic number.

It is an amenable number.

21511157 is a deficient number, since it is larger than the sum of its proper divisors (83959).

21511157 is an equidigital number, since it uses as much as digits as its factorization.

21511157 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 83958.

The product of its digits is 350, while the sum is 23.

The square root of 21511157 is about 4638.0121819590. The cubic root of 21511157 is about 278.1129787675.

Adding to 21511157 its reverse (75111512), we get a palindrome (96622669).

The spelling of 21511157 in words is "twenty-one million, five hundred eleven thousand, one hundred fifty-seven".