20690721 has 12 divisors (see below), whose sum is σ = 30993872. Its totient is φ = 13793652.

The previous prime is 20690701. The next prime is 20690737. The reversal of 20690721 is 12709602.

It is not a de Polignac number, because 20690721 - 2⁵ = 20690689 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20690701) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 42331 + ... + 42816.

Almost surely, 2^20690721 is an apocalyptic number.

It is an amenable number.

20690721 is a deficient number, since it is larger than the sum of its proper divisors (10303151).

20690721 is an frugal number, since it uses more digits than its factorization.

20690721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 85162 (or 85150 counting only the distinct ones).

The product of its (nonzero) digits is 1512, while the sum is 27.

The square root of 20690721 is about 4548.7054202267. The cubic root of 20690721 is about 274.5313052176.

The spelling of 20690721 in words is "twenty million, six hundred ninety thousand, seven hundred twenty-one".