21380409 has 16 divisors (see below), whose sum is σ = 33052800. Its totient is φ = 13633488.

The previous prime is 21380399. The next prime is 21380423. The reversal of 21380409 is 90408312.

It is not a de Polignac number, because 21380409 - 2⁸ = 21380153 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 (21380309) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16594 + ... + 17835.

It is an arithmetic number, because the mean of its divisors is an integer number (2065800).

Almost surely, 2^21380409 is an apocalyptic number.

It is an amenable number.

21380409 is a deficient number, since it is larger than the sum of its proper divisors (11672391).

21380409 is a wasteful number, since it uses less digits than its factorization.

21380409 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34461 (or 34455 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21380409 is about 4623.8954356689. The cubic root of 21380409 is about 277.5483626447.

The spelling of 21380409 in words is "twenty-one million, three hundred eighty thousand, four hundred nine".