21523973 has 4 divisors (see below), whose sum is σ = 22105740. Its totient is φ = 20942208.

The previous prime is 21523969. The next prime is 21523991. The reversal of 21523973 is 37932512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10876804 + 10647169 = 3298^2 + 3263^2 .

It is a cyclic number.

It is not a de Polignac number, because 21523973 - 2² = 21523969 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21523273) 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, 290828 + ... + 290901.

It is an arithmetic number, because the mean of its divisors is an integer number (5526435).

Almost surely, 2^21523973 is an apocalyptic number.

It is an amenable number.

21523973 is a deficient number, since it is larger than the sum of its proper divisors (581767).

21523973 is an equidigital number, since it uses as much as digits as its factorization.

21523973 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 581766.

The product of its digits is 11340, while the sum is 32.

The square root of 21523973 is about 4639.3936026166. The cubic root of 21523973 is about 278.1681995431.

The spelling of 21523973 in words is "twenty-one million, five hundred twenty-three thousand, nine hundred seventy-three".