21731139 has 8 divisors (see below), whose sum is σ = 32194320. Its totient is φ = 14487408.

The previous prime is 21731131. The next prime is 21731141. The reversal of 21731139 is 93113712.

It is not a de Polignac number, because 21731139 - 2³ = 21731131 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 804857 = 21731139 / (2 + 1 + 7 + 3 + 1 + 1 + 3 + 9).

It is not an unprimeable number, because it can be changed into a prime (21731131) 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 7 ways as a sum of consecutive naturals, for example, 402402 + ... + 402455.

It is an arithmetic number, because the mean of its divisors is an integer number (4024290).

Almost surely, 2^21731139 is an apocalyptic number.

21731139 is a deficient number, since it is larger than the sum of its proper divisors (10463181).

21731139 is an equidigital number, since it uses as much as digits as its factorization.

21731139 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 804866 (or 804860 counting only the distinct ones).

The product of its digits is 1134, while the sum is 27.

The square root of 21731139 is about 4661.6669765225. Note that the first 3 decimals coincide. The cubic root of 21731139 is about 279.0577981771.

The spelling of 21731139 in words is "twenty-one million, seven hundred thirty-one thousand, one hundred thirty-nine".