21405249 has 16 divisors (see below), whose sum is σ = 33091200. Its totient is φ = 13649328.

The previous prime is 21405247. The next prime is 21405253. The reversal of 21405249 is 94250412.

It is not a de Polignac number, because 21405249 - 2¹ = 21405247 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 (21405247) 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 15 ways as a sum of consecutive naturals, for example, 16614 + ... + 17855.

It is an arithmetic number, because the mean of its divisors is an integer number (2068200).

Almost surely, 2^21405249 is an apocalyptic number.

It is an amenable number.

21405249 is a deficient number, since it is larger than the sum of its proper divisors (11685951).

21405249 is a wasteful number, since it uses less digits than its factorization.

21405249 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34501 (or 34495 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 27.

The square root of 21405249 is about 4626.5807028517. The cubic root of 21405249 is about 277.6558073166.

The spelling of 21405249 in words is "twenty-one million, four hundred five thousand, two hundred forty-nine".