21643604 has 6 divisors (see below), whose sum is σ = 37876314. Its totient is φ = 10821800.

The previous prime is 21643519. The next prime is 21643607. The reversal of 21643604 is 40634612.

It can be written as a sum of positive squares in only one way, i.e., 21641104 + 2500 = 4652^2 + 50^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21643607) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2705447 + ... + 2705454.

It is an arithmetic number, because the mean of its divisors is an integer number (6312719).

Almost surely, 2^21643604 is an apocalyptic number.

It is an amenable number.

21643604 is a deficient number, since it is larger than the sum of its proper divisors (16232710).

21643604 is a wasteful number, since it uses less digits than its factorization.

21643604 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5410905 (or 5410903 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 26.

The square root of 21643604 is about 4652.2686938740. The cubic root of 21643604 is about 278.6826039078.

The spelling of 21643604 in words is "twenty-one million, six hundred forty-three thousand, six hundred four".