21165722640 has 240 divisors, whose sum is σ = 72210900528. Its totient is φ = 5555257344.

The previous prime is 21165722629. The next prime is 21165722671. The reversal of 21165722640 is 4622756112.

It is a happy number.

21165722640 is a `hidden beast` number, since 2 + 1 + 1 + 6 + 5 + 7 + 2 + 2 + 640 = 666.

It can be written as a sum of positive squares in 8 ways, for example, as 6682081536 + 14483641104 = 81744^2 + 120348^2 .

It is a tau number, because it is divible by the number of its divisors (240).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21165722595 and 21165722604.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 12772692 + ... + 12774348.

Almost surely, 2^21165722640 is an apocalyptic number.

21165722640 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 21165722640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36105450264).

21165722640 is an abundant number, since it is smaller than the sum of its proper divisors (51045177888).

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

21165722640 is a wasteful number, since it uses less digits than its factorization.

21165722640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1946 (or 1937 counting only the distinct ones).

The product of its (nonzero) digits is 40320, while the sum is 36.

The spelling of 21165722640 in words is "twenty-one billion, one hundred sixty-five million, seven hundred twenty-two thousand, six hundred forty".