20721439 has 2 divisors, whose sum is σ = 20721440. Its totient is φ = 20721438.

The previous prime is 20721433. The next prime is 20721461. The reversal of 20721439 is 93412702.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20721439 - 2¹⁵ = 20688671 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20721433) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10360719 + 10360720.

It is an arithmetic number, because the mean of its divisors is an integer number (10360720).

Almost surely, 2^20721439 is an apocalyptic number.

20721439 is a deficient number, since it is larger than the sum of its proper divisors (1).

20721439 is an equidigital number, since it uses as much as digits as its factorization.

20721439 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 28.

The square root of 20721439 is about 4552.0807330275. The cubic root of 20721439 is about 274.6670968890.

The spelling of 20721439 in words is "twenty million, seven hundred twenty-one thousand, four hundred thirty-nine".