21742139 has 2 divisors, whose sum is σ = 21742140. Its totient is φ = 21742138.

The previous prime is 21742111. The next prime is 21742151. The reversal of 21742139 is 93124712.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21742139 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21742159) 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 as a sum of consecutive naturals, namely, 10871069 + 10871070.

It is an arithmetic number, because the mean of its divisors is an integer number (10871070).

Almost surely, 2^21742139 is an apocalyptic number.

21742139 is a deficient number, since it is larger than the sum of its proper divisors (1).

21742139 is an equidigital number, since it uses as much as digits as its factorization.

21742139 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3024, while the sum is 29.

The square root of 21742139 is about 4662.8466627158. The cubic root of 21742139 is about 279.1048752921.

The spelling of 21742139 in words is "twenty-one million, seven hundred forty-two thousand, one hundred thirty-nine".