21531371 has 4 divisors (see below), whose sum is σ = 21804000. Its totient is φ = 21258744.

The previous prime is 21531361. The next prime is 21531379. The reversal of 21531371 is 17313512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21531371 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21531379) 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, 136196 + ... + 136353.

It is an arithmetic number, because the mean of its divisors is an integer number (5451000).

Almost surely, 2^21531371 is an apocalyptic number.

21531371 is a deficient number, since it is larger than the sum of its proper divisors (272629).

21531371 is an equidigital number, since it uses as much as digits as its factorization.

21531371 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 272628.

The product of its digits is 630, while the sum is 23.

The square root of 21531371 is about 4640.1908365928. The cubic root of 21531371 is about 278.2000656026.

Adding to 21531371 its reverse (17313512), we get a palindrome (38844883).

The spelling of 21531371 in words is "twenty-one million, five hundred thirty-one thousand, three hundred seventy-one".