21509164 has 24 divisors (see below), whose sum is σ = 39312000. Its totient is φ = 10285440.

The previous prime is 21509161. The next prime is 21509183. The reversal of 21509164 is 46190512.

It is not an unprimeable number, because it can be changed into a prime (21509161) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10062 + ... + 12010.

It is an arithmetic number, because the mean of its divisors is an integer number (1638000).

Almost surely, 2^21509164 is an apocalyptic number.

It is an amenable number.

21509164 is a deficient number, since it is larger than the sum of its proper divisors (17802836).

21509164 is a wasteful number, since it uses less digits than its factorization.

21509164 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2073 (or 2071 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21509164 is about 4637.7973220054. The cubic root of 21509164 is about 278.1043894839.

Adding to 21509164 its reverse (46190512), we get a palindrome (67699676).

The spelling of 21509164 in words is "twenty-one million, five hundred nine thousand, one hundred sixty-four".