21491723643 has 32 divisors (see below), whose sum is σ = 31604815872. Its totient is φ = 12910128000.

The previous prime is 21491723639. The next prime is 21491723653. The reversal of 21491723643 is 34632719412.

It is a happy number.

It is not a de Polignac number, because 21491723643 - 2² = 21491723639 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21491723595 and 21491723604.

It is not an unprimeable number, because it can be changed into a prime (21491723623) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 241246 + ... + 318092.

It is an arithmetic number, because the mean of its divisors is an integer number (987650496).

Almost surely, 2^21491723643 is an apocalyptic number.

21491723643 is a deficient number, since it is larger than the sum of its proper divisors (10113092229).

21491723643 is a wasteful number, since it uses less digits than its factorization.

21491723643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 77035.

The product of its digits is 217728, while the sum is 42.

The spelling of 21491723643 in words is "twenty-one billion, four hundred ninety-one million, seven hundred twenty-three thousand, six hundred forty-three".