21537396 has 18 divisors (see below), whose sum is σ = 54441842. Its totient is φ = 7179120.

The previous prime is 21537391. The next prime is 21537427. The reversal of 21537396 is 69373512.

It can be written as a sum of positive squares in only one way, i.e., 12320100 + 9217296 = 3510^2 + 3036^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 598261 = 21537396 / (2 + 1 + 5 + 3 + 7 + 3 + 9 + 6).

It is a self number, because there is not a number n which added to its sum of digits gives 21537396.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21537391) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 299095 + ... + 299166.

Almost surely, 2^21537396 is an apocalyptic number.

It is an amenable number.

21537396 is an abundant number, since it is smaller than the sum of its proper divisors (32904446).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21537396 is a wasteful number, since it uses less digits than its factorization.

21537396 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 598271 (or 598266 counting only the distinct ones).

The product of its digits is 34020, while the sum is 36.

The square root of 21537396 is about 4640.8400101706. The cubic root of 21537396 is about 278.2260122253.

The spelling of 21537396 in words is "twenty-one million, five hundred thirty-seven thousand, three hundred ninety-six".