21609918 has 24 divisors (see below), whose sum is σ = 51078456. Its totient is φ = 6548400.

The previous prime is 21609899. The next prime is 21609919. The reversal of 21609918 is 81990612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21609919) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 54373 + ... + 54768.

It is an arithmetic number, because the mean of its divisors is an integer number (2128269).

Almost surely, 2^21609918 is an apocalyptic number.

21609918 is an abundant number, since it is smaller than the sum of its proper divisors (29468538).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21609918 is a wasteful number, since it uses less digits than its factorization.

21609918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109160 (or 109157 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 36.

The square root of 21609918 is about 4648.6468999054. The cubic root of 21609918 is about 278.5379487519.

The spelling of 21609918 in words is "twenty-one million, six hundred nine thousand, nine hundred eighteen".