21372309 has 16 divisors (see below), whose sum is σ = 36186240. Its totient is φ = 12212640.

The previous prime is 21372293. The next prime is 21372317. The reversal of 21372309 is 90327312.

It is not a de Polignac number, because 21372309 - 2⁴ = 21372293 is a prime.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21377309) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 56352 + ... + 56729.

It is an arithmetic number, because the mean of its divisors is an integer number (2261640).

Almost surely, 2^21372309 is an apocalyptic number.

It is an amenable number.

21372309 is a deficient number, since it is larger than the sum of its proper divisors (14813931).

21372309 is a wasteful number, since it uses less digits than its factorization.

21372309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 113097 (or 113091 counting only the distinct ones).

The product of its (nonzero) digits is 2268, while the sum is 27.

The square root of 21372309 is about 4623.0194678370. The cubic root of 21372309 is about 277.5133083464.

The spelling of 21372309 in words is "twenty-one million, three hundred seventy-two thousand, three hundred nine".