21491857756 has 6 divisors (see below), whose sum is σ = 37610751080. Its totient is φ = 10745928876.

The previous prime is 21491857729. The next prime is 21491857781. The reversal of 21491857756 is 65775819412.

It is a junction number, because it is equal to n+sod(n) for n = 21491857697 and 21491857706.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2686482216 + ... + 2686482223.

Almost surely, 2^21491857756 is an apocalyptic number.

It is an amenable number.

21491857756 is a deficient number, since it is larger than the sum of its proper divisors (16118893324).

21491857756 is a wasteful number, since it uses less digits than its factorization.

21491857756 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5372964443 (or 5372964441 counting only the distinct ones).

The product of its digits is 4233600, while the sum is 55.

The spelling of 21491857756 in words is "twenty-one billion, four hundred ninety-one million, eight hundred fifty-seven thousand, seven hundred fifty-six".