21706020640 has 24 divisors (see below), whose sum is σ = 51280474140. Its totient is φ = 8682408192.

The previous prime is 21706020629. The next prime is 21706020647. The reversal of 21706020640 is 4602060712.

It can be written as a sum of positive squares in 2 ways, for example, as 21476316304 + 229704336 = 146548^2 + 15156^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21706020599 and 21706020608.

It is not an unprimeable number, because it can be changed into a prime (21706020647) 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, 67831155 + ... + 67831474.

Almost surely, 2^21706020640 is an apocalyptic number.

21706020640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21706020640 is an abundant number, since it is smaller than the sum of its proper divisors (29574453500).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21706020640 is a wasteful number, since it uses less digits than its factorization.

21706020640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 135662644 (or 135662636 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 28.

The spelling of 21706020640 in words is "twenty-one billion, seven hundred six million, twenty thousand, six hundred forty".