21043637 has 16 divisors (see below), whose sum is σ = 23357952. Its totient is φ = 18869760.

The previous prime is 21043613. The next prime is 21043661. The reversal of 21043637 is 73634012.

It is an interprime number because it is at equal distance from previous prime (21043613) and next prime (21043661).

It is a cyclic number.

It is not a de Polignac number, because 21043637 - 2⁸ = 21043381 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21043667) 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 15 ways as a sum of consecutive naturals, for example, 38198 + ... + 38744.

It is an arithmetic number, because the mean of its divisors is an integer number (1459872).

Almost surely, 2^21043637 is an apocalyptic number.

It is an amenable number.

21043637 is a deficient number, since it is larger than the sum of its proper divisors (2314315).

21043637 is a wasteful number, since it uses less digits than its factorization.

21043637 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 668.

The product of its (nonzero) digits is 3024, while the sum is 26.

The square root of 21043637 is about 4587.3344111804. The cubic root of 21043637 is about 276.0833825292.

Adding to 21043637 its reverse (73634012), we get a palindrome (94677649).

The spelling of 21043637 in words is "twenty-one million, forty-three thousand, six hundred thirty-seven".