21649903 has 4 divisors (see below), whose sum is σ = 23618088. Its totient is φ = 19681720.

The previous prime is 21649883. The next prime is 21649909. The reversal of 21649903 is 30994612.

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 21649903 - 2²¹ = 19552751 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 (21649909) 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, 984076 + ... + 984097.

It is an arithmetic number, because the mean of its divisors is an integer number (5904522).

Almost surely, 2^21649903 is an apocalyptic number.

21649903 is a deficient number, since it is larger than the sum of its proper divisors (1968185).

21649903 is a wasteful number, since it uses less digits than its factorization.

21649903 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1968184.

The product of its (nonzero) digits is 11664, while the sum is 34.

The square root of 21649903 is about 4652.9456261598. The cubic root of 21649903 is about 278.7096365507.

The spelling of 21649903 in words is "twenty-one million, six hundred forty-nine thousand, nine hundred three".