21561744816 has 60 divisors (see below), whose sum is σ = 61626850272. Its totient is φ = 7034325888.

The previous prime is 21561744803. The next prime is 21561744817. The reversal of 21561744816 is 61844716512.

21561744816 is a `hidden beast` number, since 2 + 1 + 561 + 7 + 4 + 4 + 81 + 6 = 666.

It is not an unprimeable number, because it can be changed into a prime (21561744817) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1586151 + ... + 1599686.

Almost surely, 2^21561744816 is an apocalyptic number.

It is an amenable number.

21561744816 is an abundant number, since it is smaller than the sum of its proper divisors (40065105456).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21561744816 is a wasteful number, since it uses less digits than its factorization.

21561744816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3185898 (or 3185889 counting only the distinct ones).

The product of its digits is 322560, while the sum is 45.

The spelling of 21561744816 in words is "twenty-one billion, five hundred sixty-one million, seven hundred forty-four thousand, eight hundred sixteen".