21491984664 has 80 divisors (see below), whose sum is σ = 63738516600. Its totient is φ = 6742579968.

The previous prime is 21491984663. The next prime is 21491984669. The reversal of 21491984664 is 46648919412.

21491984664 is a `hidden beast` number, since 2 + 1 + 4 + 91 + 98 + 466 + 4 = 666.

It is a super-2 number, since 2×21491984664² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 21491984664.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21491984663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 964474 + ... + 986505.

Almost surely, 2^21491984664 is an apocalyptic number.

21491984664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21491984664 is an abundant number, since it is smaller than the sum of its proper divisors (42246531936).

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

21491984664 is a wasteful number, since it uses less digits than its factorization.

21491984664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1951014 (or 1951001 counting only the distinct ones).

The product of its digits is 2985984, while the sum is 54.

The spelling of 21491984664 in words is "twenty-one billion, four hundred ninety-one million, nine hundred eighty-four thousand, six hundred sixty-four".