20729991 has 4 divisors (see below), whose sum is σ = 27639992. Its totient is φ = 13819992.

The previous prime is 20729981. The next prime is 20729993. The reversal of 20729991 is 19992702.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 20729991 - 2⁶ = 20729927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20729993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3454996 + ... + 3455001.

It is an arithmetic number, because the mean of its divisors is an integer number (6909998).

Almost surely, 2^20729991 is an apocalyptic number.

20729991 is a deficient number, since it is larger than the sum of its proper divisors (6910001).

20729991 is an equidigital number, since it uses as much as digits as its factorization.

20729991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6910000.

The product of its (nonzero) digits is 20412, while the sum is 39.

The square root of 20729991 is about 4553.0199867780. The cubic root of 20729991 is about 274.7048778871.

The spelling of 20729991 in words is "twenty million, seven hundred twenty-nine thousand, nine hundred ninety-one".