21491516738 has 8 divisors (see below), whose sum is σ = 32371040460. Its totient is φ = 10701169920.

The previous prime is 21491516663. The next prime is 21491516743. The reversal of 21491516738 is 83761519412.

It can be written as a sum of positive squares in 2 ways, for example, as 21172287049 + 319229689 = 145507^2 + 17867^2 .

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

It is a junction number, because it is equal to n+sod(n) for n = 21491516692 and 21491516701.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22293623 + ... + 22294586.

Almost surely, 2^21491516738 is an apocalyptic number.

21491516738 is a deficient number, since it is larger than the sum of its proper divisors (10879523722).

21491516738 is a wasteful number, since it uses less digits than its factorization.

21491516738 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44588452.

The product of its digits is 362880, while the sum is 47.

The spelling of 21491516738 in words is "twenty-one billion, four hundred ninety-one million, five hundred sixteen thousand, seven hundred thirty-eight".