21157819 has 4 divisors (see below), whose sum is σ = 21324544. Its totient is φ = 20991096.

The previous prime is 21157817. The next prime is 21157831. The reversal of 21157819 is 91875112.

It is a happy number.

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 21157819 - 2¹ = 21157817 is a prime.

It is a super-2 number, since 2×21157819² = 895306609673522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21157817) 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, 83172 + ... + 83425.

It is an arithmetic number, because the mean of its divisors is an integer number (5331136).

Almost surely, 2^21157819 is an apocalyptic number.

21157819 is a deficient number, since it is larger than the sum of its proper divisors (166725).

21157819 is a wasteful number, since it uses less digits than its factorization.

21157819 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 166724.

The product of its digits is 5040, while the sum is 34.

The square root of 21157819 is about 4599.7629286736. The cubic root of 21157819 is about 276.5818215341.

The spelling of 21157819 in words is "twenty-one million, one hundred fifty-seven thousand, eight hundred nineteen".