21715922981 has 4 divisors (see below), whose sum is σ = 22013401452. Its totient is φ = 21418444512.

The previous prime is 21715922971. The next prime is 21715922983. The reversal of 21715922981 is 18922951712.

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

It can be written as a sum of positive squares in 2 ways, for example, as 7107333025 + 14608589956 = 84305^2 + 120866^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21715922981 is a prime.

It is a super-2 number, since 2×21715922981² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21715922983) 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, 148739126 + ... + 148739271.

It is an arithmetic number, because the mean of its divisors is an integer number (5503350363).

Almost surely, 2^21715922981 is an apocalyptic number.

It is an amenable number.

21715922981 is a deficient number, since it is larger than the sum of its proper divisors (297478471).

21715922981 is an equidigital number, since it uses as much as digits as its factorization.

21715922981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 297478470.

The product of its digits is 181440, while the sum is 47.

The spelling of 21715922981 in words is "twenty-one billion, seven hundred fifteen million, nine hundred twenty-two thousand, nine hundred eighty-one".