21050909 has 4 divisors (see below), whose sum is σ = 22964640. Its totient is φ = 19137180.

The previous prime is 21050873. The next prime is 21050921. The reversal of 21050909 is 90905012.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21050909 - 2¹⁶ = 20985373 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21050929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 956849 + ... + 956870.

It is an arithmetic number, because the mean of its divisors is an integer number (5741160).

Almost surely, 2^21050909 is an apocalyptic number.

It is an amenable number.

21050909 is a deficient number, since it is larger than the sum of its proper divisors (1913731).

21050909 is a wasteful number, since it uses less digits than its factorization.

21050909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1913730.

The product of its (nonzero) digits is 810, while the sum is 26.

The square root of 21050909 is about 4588.1269598824. The cubic root of 21050909 is about 276.1151806944.

The spelling of 21050909 in words is "twenty-one million, fifty thousand, nine hundred nine".