20721603 has 16 divisors (see below), whose sum is σ = 31933440. Its totient is φ = 11706816.

The previous prime is 20721599. The next prime is 20721611. The reversal of 20721603 is 30612702.

It is a happy number.

It is not a de Polignac number, because 20721603 - 2² = 20721599 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a self number, because there is not a number n which added to its sum of digits gives 20721603.

It is not an unprimeable number, because it can be changed into a prime (20721683) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3675 + ... + 7412.

It is an arithmetic number, because the mean of its divisors is an integer number (1995840).

Almost surely, 2^20721603 is an apocalyptic number.

20721603 is a deficient number, since it is larger than the sum of its proper divisors (11211837).

20721603 is a wasteful number, since it uses less digits than its factorization.

20721603 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11186.

The product of its (nonzero) digits is 504, while the sum is 21.

The square root of 20721603 is about 4552.0987467321. The cubic root of 20721603 is about 274.6678215054.

The spelling of 20721603 in words is "twenty million, seven hundred twenty-one thousand, six hundred three".