21531237 has 48 divisors (see below), whose sum is σ = 37920960. Its totient is φ = 10741248.

The previous prime is 21531233. The next prime is 21531269. The reversal of 21531237 is 73213512.

It is not a de Polignac number, because 21531237 - 2² = 21531233 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531233) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 36013 + ... + 36605.

It is an arithmetic number, because the mean of its divisors is an integer number (790020).

Almost surely, 2^21531237 is an apocalyptic number.

It is an amenable number.

21531237 is a deficient number, since it is larger than the sum of its proper divisors (16389723).

21531237 is a wasteful number, since it uses less digits than its factorization.

21531237 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 642 (or 635 counting only the distinct ones).

The product of its digits is 1260, while the sum is 24.

The square root of 21531237 is about 4640.1763975090. The cubic root of 21531237 is about 278.1994884775.

Adding to 21531237 its reverse (73213512), we get a palindrome (94744749).

The spelling of 21531237 in words is "twenty-one million, five hundred thirty-one thousand, two hundred thirty-seven".