21907809 has 48 divisors (see below), whose sum is σ = 39970944. Its totient is φ = 11232000.

The previous prime is 21907763. The next prime is 21907813. The reversal of 21907809 is 90870912.

It is a happy number.

It is not a de Polignac number, because 21907809 - 2¹¹ = 21905761 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21907829) 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 47 ways as a sum of consecutive naturals, for example, 69837 + ... + 70149.

It is an arithmetic number, because the mean of its divisors is an integer number (832728).

Almost surely, 2^21907809 is an apocalyptic number.

It is an amenable number.

21907809 is a deficient number, since it is larger than the sum of its proper divisors (18063135).

21907809 is a wasteful number, since it uses less digits than its factorization.

21907809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 438 (or 435 counting only the distinct ones).

The product of its (nonzero) digits is 9072, while the sum is 36.

The square root of 21907809 is about 4680.5778489413. The cubic root of 21907809 is about 279.8119868773.

It can be divided in two parts, 2190 and 7809, that added together give a palindrome (9999).

The spelling of 21907809 in words is "twenty-one million, nine hundred seven thousand, eight hundred nine".