21158437 has 4 divisors (see below), whose sum is σ = 21170476. Its totient is φ = 21146400.

The previous prime is 21158377. The next prime is 21158471. The reversal of 21158437 is 73485112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 10719076 + 10439361 = 3274^2 + 3231^2 .

It is a cyclic number.

It is not a de Polignac number, because 21158437 - 2¹⁵ = 21125669 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21158399 and 21158408.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21158737) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2814 + ... + 7087.

It is an arithmetic number, because the mean of its divisors is an integer number (5292619).

Almost surely, 2^21158437 is an apocalyptic number.

It is an amenable number.

21158437 is a deficient number, since it is larger than the sum of its proper divisors (12039).

21158437 is an equidigital number, since it uses as much as digits as its factorization.

21158437 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12038.

The product of its digits is 6720, while the sum is 31.

The square root of 21158437 is about 4599.8301055582. The cubic root of 21158437 is about 276.5845144062.

The spelling of 21158437 in words is "twenty-one million, one hundred fifty-eight thousand, four hundred thirty-seven".