21651020720 has 40 divisors (see below), whose sum is σ = 57529856544. Its totient is φ = 7423206912.

The previous prime is 21651020683. The next prime is 21651020723. The reversal of 21651020720 is 2702015612.

It is a tau number, because it is divible by the number of its divisors (40).

It is a self number, because there is not a number n which added to its sum of digits gives 21651020720.

It is not an unprimeable number, because it can be changed into a prime (21651020723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19330709 + ... + 19331828.

Almost surely, 2^21651020720 is an apocalyptic number.

21651020720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21651020720 is an abundant number, since it is smaller than the sum of its proper divisors (35878835824).

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

21651020720 is a wasteful number, since it uses less digits than its factorization.

21651020720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38662557 (or 38662551 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 26.

The spelling of 21651020720 in words is "twenty-one billion, six hundred fifty-one million, twenty thousand, seven hundred twenty".