21601909 has 16 divisors (see below), whose sum is σ = 25214976. Its totient is φ = 18126000.

The previous prime is 21601903. The next prime is 21601913. The reversal of 21601909 is 90910612.

It is a cyclic number.

It is not a de Polignac number, because 21601909 - 2⁹ = 21601397 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 (21601903) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 113004 + ... + 113194.

It is an arithmetic number, because the mean of its divisors is an integer number (1575936).

Almost surely, 2^21601909 is an apocalyptic number.

It is an amenable number.

21601909 is a deficient number, since it is larger than the sum of its proper divisors (3613067).

21601909 is a wasteful number, since it uses less digits than its factorization.

21601909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 456.

The product of its (nonzero) digits is 972, while the sum is 28.

The square root of 21601909 is about 4647.7853866116. The cubic root of 21601909 is about 278.5035342131.

The spelling of 21601909 in words is "twenty-one million, six hundred one thousand, nine hundred nine".