21664350720 has 400 divisors, whose sum is σ = 78143712768. Its totient is φ = 5736407040.

The previous prime is 21664350709. The next prime is 21664350731. The reversal of 21664350720 is 2705346612.

21664350720 is a `hidden beast` number, since 2 + 1 + 6 + 643 + 5 + 0 + 7 + 2 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (21664350709) and next prime (21664350731).

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

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 39605487 + ... + 39606033.

Almost surely, 2^21664350720 is an apocalyptic number.

21664350720 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 21664350720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39071856384).

21664350720 is an abundant number, since it is smaller than the sum of its proper divisors (56479362048).

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

21664350720 is an equidigital number, since it uses as much as digits as its factorization.

21664350720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 773 (or 748 counting only the distinct ones).

The product of its (nonzero) digits is 60480, while the sum is 36.

The spelling of 21664350720 in words is "twenty-one billion, six hundred sixty-four million, three hundred fifty thousand, seven hundred twenty".