21781359 has 16 divisors (see below), whose sum is σ = 32454240. Its totient is φ = 14437440.

The previous prime is 21781337. The next prime is 21781363. The reversal of 21781359 is 95318712.

It is not a de Polignac number, because 21781359 - 2¹¹ = 21779311 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21781379) 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, 2659 + ... + 7115.

It is an arithmetic number, because the mean of its divisors is an integer number (2028390).

Almost surely, 2^21781359 is an apocalyptic number.

21781359 is a deficient number, since it is larger than the sum of its proper divisors (10672881).

21781359 is a wasteful number, since it uses less digits than its factorization.

21781359 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4647 (or 4641 counting only the distinct ones).

The product of its digits is 15120, while the sum is 36.

The square root of 21781359 is about 4667.0503532745. The cubic root of 21781359 is about 279.2725974863.

The spelling of 21781359 in words is "twenty-one million, seven hundred eighty-one thousand, three hundred fifty-nine".