21291897 has 16 divisors (see below), whose sum is σ = 31066560. Its totient is φ = 12864000.

The previous prime is 21291889. The next prime is 21291899. The reversal of 21291897 is 79819212.

It is not a de Polignac number, because 21291897 - 2³ = 21291889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21291899) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12429 + ... + 14037.

It is an arithmetic number, because the mean of its divisors is an integer number (1941660).

Almost surely, 2^21291897 is an apocalyptic number.

It is an amenable number.

21291897 is a deficient number, since it is larger than the sum of its proper divisors (9774663).

21291897 is a wasteful number, since it uses less digits than its factorization.

21291897 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2024.

The product of its digits is 18144, while the sum is 39.

The square root of 21291897 is about 4614.3143586019. The cubic root of 21291897 is about 277.1648286763.

The spelling of 21291897 in words is "twenty-one million, two hundred ninety-one thousand, eight hundred ninety-seven".