21129739 has 2 divisors, whose sum is σ = 21129740. Its totient is φ = 21129738.

The previous prime is 21129737. The next prime is 21129749. The reversal of 21129739 is 93792112.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21129739 - 2¹ = 21129737 is a prime.

Together with 21129737, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21129737) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10564869 + 10564870.

It is an arithmetic number, because the mean of its divisors is an integer number (10564870).

Almost surely, 2^21129739 is an apocalyptic number.

21129739 is a deficient number, since it is larger than the sum of its proper divisors (1).

21129739 is an equidigital number, since it uses as much as digits as its factorization.

21129739 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6804, while the sum is 34.

The square root of 21129739 is about 4596.7095840394. The cubic root of 21129739 is about 276.4594104314.

The spelling of 21129739 in words is "twenty-one million, one hundred twenty-nine thousand, seven hundred thirty-nine".