21609871 has 4 divisors (see below), whose sum is σ = 21976200. Its totient is φ = 21243544.

The previous prime is 21609869. The next prime is 21609877. The reversal of 21609871 is 17890612.

It is a happy number.

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 21609871 - 2¹ = 21609869 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 (21609877) 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, 183076 + ... + 183193.

It is an arithmetic number, because the mean of its divisors is an integer number (5494050).

Almost surely, 2^21609871 is an apocalyptic number.

21609871 is a deficient number, since it is larger than the sum of its proper divisors (366329).

21609871 is an equidigital number, since it uses as much as digits as its factorization.

21609871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 366328.

The product of its (nonzero) digits is 6048, while the sum is 34.

The square root of 21609871 is about 4648.6418446682. The cubic root of 21609871 is about 278.5377468184.

The spelling of 21609871 in words is "twenty-one million, six hundred nine thousand, eight hundred seventy-one".