20721438506 has 16 divisors (see below), whose sum is σ = 31786797384. Its totient is φ = 10128351744.

The previous prime is 20721438503. The next prime is 20721438509. The reversal of 20721438506 is 60583412702.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (20721438503) and next prime (20721438509).

It can be written as a sum of positive squares in 4 ways, for example, as 16729094281 + 3992344225 = 129341^2 + 63185^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 20721438506.

It is not an unprimeable number, because it can be changed into a prime (20721438503) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 611501 + ... + 644496.

Almost surely, 2^20721438506 is an apocalyptic number.

20721438506 is a deficient number, since it is larger than the sum of its proper divisors (11065358878).

20721438506 is a wasteful number, since it uses less digits than its factorization.

20721438506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1256185.

The product of its (nonzero) digits is 80640, while the sum is 38.

The spelling of 20721438506 in words is "twenty billion, seven hundred twenty-one million, four hundred thirty-eight thousand, five hundred six".