21323909 has 6 divisors (see below), whose sum is σ = 22505670. Its totient is φ = 20201256.

The previous prime is 21323893. The next prime is 21323941. The reversal of 21323909 is 90932312.

It can be written as a sum of positive squares in only one way, i.e., 19936225 + 1387684 = 4465^2 + 1178^2 .

It is not a de Polignac number, because 21323909 - 2⁴ = 21323893 is a prime.

It is a super-4 number, since 4×21323909⁴ (a number of 30 digits) contains 4444 as substring. Note that it is a super-d number also for d = 3.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21323959) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 29174 + ... + 29895.

It is an arithmetic number, because the mean of its divisors is an integer number (3750945).

Almost surely, 2^21323909 is an apocalyptic number.

It is an amenable number.

21323909 is a deficient number, since it is larger than the sum of its proper divisors (1181761).

21323909 is an equidigital number, since it uses as much as digits as its factorization.

21323909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59107 (or 59088 counting only the distinct ones).

The product of its (nonzero) digits is 2916, while the sum is 29.

The square root of 21323909 is about 4617.7818268082. The cubic root of 21323909 is about 277.3036633013.

The spelling of 21323909 in words is "twenty-one million, three hundred twenty-three thousand, nine hundred nine".