21564260640 has 480 divisors, whose sum is σ = 86790599280. Its totient is φ = 4995219456.

The previous prime is 21564260629. The next prime is 21564260647. The reversal of 21564260640 is 4606246512.

21564260640 is a `hidden beast` number, since 2 + 1 + 5 + 6 + 4 + 2 + 6 + 0 + 640 = 666.

It can be written as a sum of positive squares in 8 ways, for example, as 6485403024 + 15078857616 = 80532^2 + 122796^2 .

It is a tau number, because it is divible by the number of its divisors (480).

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 = 21564260595 and 21564260604.

It is not an unprimeable number, because it can be changed into a prime (21564260647) by changing a digit.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 2860396 + ... + 2867924.

Almost surely, 2^21564260640 is an apocalyptic number.

21564260640 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 21564260640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43395299640).

21564260640 is an abundant number, since it is smaller than the sum of its proper divisors (65226338640).

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

21564260640 is a wasteful number, since it uses less digits than its factorization.

21564260640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7586 (or 7569 counting only the distinct ones).

The product of its (nonzero) digits is 69120, while the sum is 36.

The spelling of 21564260640 in words is "twenty-one billion, five hundred sixty-four million, two hundred sixty thousand, six hundred forty".