21081878416 has 15 divisors (see below), whose sum is σ = 40847264731. Its totient is φ = 10540648816.

The previous prime is 21081878413. The next prime is 21081878429. The reversal of 21081878416 is 61487818012.

The square root of 21081878416 is 145196.

It is a perfect power (a square), and thus also a powerful number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21081878413) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 562635 + ... + 598933.

Almost surely, 2^21081878416 is an apocalyptic number.

21081878416 is the 145196-th square number.

It is an amenable number.

21081878416 is a deficient number, since it is larger than the sum of its proper divisors (19765386315).

21081878416 is an frugal number, since it uses more digits than its factorization.

21081878416 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72606 (or 36301 counting only the distinct ones).

The product of its (nonzero) digits is 172032, while the sum is 46.

The spelling of 21081878416 in words is "twenty-one billion, eighty-one million, eight hundred seventy-eight thousand, four hundred sixteen".