21708139 has 2 divisors, whose sum is σ = 21708140. Its totient is φ = 21708138.

The previous prime is 21708121. The next prime is 21708151. The reversal of 21708139 is 93180712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21708139 - 2⁵ = 21708107 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21708139.

It is not a weakly prime, because it can be changed into another prime (21708539) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10854069 + 10854070.

It is an arithmetic number, because the mean of its divisors is an integer number (10854070).

Almost surely, 2^21708139 is an apocalyptic number.

21708139 is a deficient number, since it is larger than the sum of its proper divisors (1).

21708139 is an equidigital number, since it uses as much as digits as its factorization.

21708139 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21708139 is about 4659.1993947458. The cubic root of 21708139 is about 278.9593128491.

The spelling of 21708139 in words is "twenty-one million, seven hundred eight thousand, one hundred thirty-nine".