21506371 has 4 divisors (see below), whose sum is σ = 22248000. Its totient is φ = 20764744.

The previous prime is 21506369. The next prime is 21506389. The reversal of 21506371 is 17360512.

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

It is a cyclic number.

It is not a de Polignac number, because 21506371 - 2¹ = 21506369 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21506341) 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, 370771 + ... + 370828.

It is an arithmetic number, because the mean of its divisors is an integer number (5562000).

Almost surely, 2^21506371 is an apocalyptic number.

21506371 is a deficient number, since it is larger than the sum of its proper divisors (741629).

21506371 is an equidigital number, since it uses as much as digits as its factorization.

21506371 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 741628.

The product of its (nonzero) digits is 1260, while the sum is 25.

The square root of 21506371 is about 4637.4961994594. The cubic root of 21506371 is about 278.0923515268.

Adding to 21506371 its reverse (17360512), we get a palindrome (38866883).

The spelling of 21506371 in words is "twenty-one million, five hundred six thousand, three hundred seventy-one".