21654306640 has 80 divisors (see below), whose sum is σ = 50935164048. Its totient is φ = 8561000448.

The previous prime is 21654306637. The next prime is 21654306659. The reversal of 21654306640 is 4660345612.

It can be written as a sum of positive squares in 8 ways, for example, as 3940826176 + 17713480464 = 62776^2 + 133092^2 .

It is a tau number, because it is divible by the number of its divisors (80).

It is a self number, because there is not a number n which added to its sum of digits gives 21654306640.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2419614 + ... + 2428546.

Almost surely, 2^21654306640 is an apocalyptic number.

21654306640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21654306640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25467582024).

21654306640 is an abundant number, since it is smaller than the sum of its proper divisors (29280857408).

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

21654306640 is a wasteful number, since it uses less digits than its factorization.

21654306640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9296 (or 9290 counting only the distinct ones).

The product of its (nonzero) digits is 103680, while the sum is 37.

The spelling of 21654306640 in words is "twenty-one billion, six hundred fifty-four million, three hundred six thousand, six hundred forty".