20721499 has 4 divisors (see below), whose sum is σ = 20731840. Its totient is φ = 20711160.

The previous prime is 20721497. The next prime is 20721509. The reversal of 20721499 is 99412702.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 20721499 - 2¹ = 20721497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20721497) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1092 + ... + 6529.

It is an arithmetic number, because the mean of its divisors is an integer number (5182960).

Almost surely, 2^20721499 is an apocalyptic number.

20721499 is a deficient number, since it is larger than the sum of its proper divisors (10341).

20721499 is an equidigital number, since it uses as much as digits as its factorization.

20721499 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10340.

The product of its (nonzero) digits is 9072, while the sum is 34.

The square root of 20721499 is about 4552.0873234155. The cubic root of 20721499 is about 274.6673619930.

The spelling of 20721499 in words is "twenty million, seven hundred twenty-one thousand, four hundred ninety-nine".