21781039 has 12 divisors (see below), whose sum is σ = 25818264. Its totient is φ = 18315024.

The previous prime is 21781021. The next prime is 21781093. The reversal of 21781039 is 93018712.

It is not a de Polignac number, because 21781039 - 2¹⁷ = 21649967 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21781039.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21781139) 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 11 ways as a sum of consecutive naturals, for example, 1597 + ... + 6790.

It is an arithmetic number, because the mean of its divisors is an integer number (2151522).

Almost surely, 2^21781039 is an apocalyptic number.

21781039 is a deficient number, since it is larger than the sum of its proper divisors (4037225).

21781039 is an equidigital number, since it uses as much as digits as its factorization.

21781039 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8454 (or 8447 counting only the distinct ones).

The product of its (nonzero) digits is 3024, while the sum is 31.

The square root of 21781039 is about 4667.0160702530. The cubic root of 21781039 is about 279.2712298387.

The spelling of 21781039 in words is "twenty-one million, seven hundred eighty-one thousand, thirty-nine".