21309345 has 32 divisors (see below), whose sum is σ = 39196800. Its totient is φ = 10971072.

The previous prime is 21309341. The next prime is 21309383. The reversal of 21309345 is 54390312.

It is not a de Polignac number, because 21309345 - 2² = 21309341 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21309341) 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 31 ways as a sum of consecutive naturals, for example, 1194 + ... + 6636.

It is an arithmetic number, because the mean of its divisors is an integer number (1224900).

Almost surely, 2^21309345 is an apocalyptic number.

It is an amenable number.

21309345 is a deficient number, since it is larger than the sum of its proper divisors (17887455).

21309345 is a wasteful number, since it uses less digits than its factorization.

21309345 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5486 (or 5480 counting only the distinct ones).

The product of its (nonzero) digits is 3240, while the sum is 27.

The square root of 21309345 is about 4616.2046098500. The cubic root of 21309345 is about 277.2405171187.

Adding to 21309345 its reverse (54390312), we get a palindrome (75699657).

The spelling of 21309345 in words is "twenty-one million, three hundred nine thousand, three hundred forty-five".