21538778720 has 96 divisors (see below), whose sum is σ = 53351343360. Its totient is φ = 8201571840.

The previous prime is 21538778683. The next prime is 21538778749. The reversal of 21538778720 is 2787783512.

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, 762611 + ... + 790349.

It is an arithmetic number, because the mean of its divisors is an integer number (555743160).

Almost surely, 2^21538778720 is an apocalyptic number.

21538778720 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 21538778720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26675671680).

21538778720 is an abundant number, since it is smaller than the sum of its proper divisors (31812564640).

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

21538778720 is a wasteful number, since it uses less digits than its factorization.

21538778720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27988 (or 27980 counting only the distinct ones).

The product of its (nonzero) digits is 1317120, while the sum is 50.

The spelling of 21538778720 in words is "twenty-one billion, five hundred thirty-eight million, seven hundred seventy-eight thousand, seven hundred twenty".