21491857757 has 8 divisors (see below), whose sum is σ = 21849475800. Its totient is φ = 21134410560.

The previous prime is 21491857729. The next prime is 21491857781. The reversal of 21491857757 is 75775819412.

It can be written as a sum of positive squares in 4 ways, for example, as 5540420356 + 15951437401 = 74434^2 + 126299^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21491857757 - 2¹⁰ = 21491856733 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21491857157) 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, 224783 + ... + 305795.

It is an arithmetic number, because the mean of its divisors is an integer number (2731184475).

Almost surely, 2^21491857757 is an apocalyptic number.

It is an amenable number.

21491857757 is a deficient number, since it is larger than the sum of its proper divisors (357618043).

21491857757 is an equidigital number, since it uses as much as digits as its factorization.

21491857757 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 85423.

The product of its digits is 4939200, while the sum is 56.

The spelling of 21491857757 in words is "twenty-one billion, four hundred ninety-one million, eight hundred fifty-seven thousand, seven hundred fifty-seven".