21297664 has 20 divisors (see below), whose sum is σ = 42554754. Its totient is φ = 10648576.

The previous prime is 21297659. The next prime is 21297667. The reversal of 21297664 is 46679212.

It can be written as a sum of positive squares in only one way, i.e., 19360000 + 1937664 = 4400^2 + 1392^2 .

It is not an unprimeable number, because it can be changed into a prime (21297667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20287 + ... + 21310.

Almost surely, 2^21297664 is an apocalyptic number.

It is an amenable number.

21297664 is a deficient number, since it is larger than the sum of its proper divisors (21257090).

21297664 is an frugal number, since it uses more digits than its factorization.

21297664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41615 (or 41599 counting only the distinct ones).

The product of its digits is 36288, while the sum is 37.

The square root of 21297664 is about 4614.9392195347. The cubic root of 21297664 is about 277.1898501712.

The spelling of 21297664 in words is "twenty-one million, two hundred ninety-seven thousand, six hundred sixty-four".