21139709 has 2 divisors, whose sum is σ = 21139710. Its totient is φ = 21139708.

The previous prime is 21139667. The next prime is 21139711. The reversal of 21139709 is 90793112.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14364100 + 6775609 = 3790^2 + 2603^2 .

It is a cyclic number.

It is not a de Polignac number, because 21139709 - 2⁸ = 21139453 is a prime.

Together with 21139711, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21139009) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10569854 + 10569855.

It is an arithmetic number, because the mean of its divisors is an integer number (10569855).

Almost surely, 2^21139709 is an apocalyptic number.

It is an amenable number.

21139709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21139709 is an equidigital number, since it uses as much as digits as its factorization.

21139709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3402, while the sum is 32.

The square root of 21139709 is about 4597.7939275265. The cubic root of 21139709 is about 276.5028857581.

The spelling of 21139709 in words is "twenty-one million, one hundred thirty-nine thousand, seven hundred nine".