21721724743680 has 2496 divisors, whose sum is σ = 90882576046080. Its totient is φ = 4930456780800.

The previous prime is 21721724743637. The next prime is 21721724743723. The reversal of 21721724743680 is 8634742712712.

It is a happy number.

21721724743680 is a `hidden beast` number, since 2 + 1 + 7 + 21 + 72 + 47 + 436 + 80 = 666.

21721724743680 is digitally balanced in base 5, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (21721724743637) and next prime (21721724743723).

It is a tau number, because it is divible by the number of its divisors (2496).

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 191 ways as a sum of consecutive naturals, for example, 50398433065 + ... + 50398433495.

It is an arithmetic number, because the mean of its divisors is an integer number (36411288480).

Almost surely, 2^{21721724743680} is an apocalyptic number.

21721724743680 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 21721724743680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (45441288023040).

21721724743680 is an abundant number, since it is smaller than the sum of its proper divisors (69160851302400).

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

21721724743680 is a wasteful number, since it uses less digits than its factorization.

21721724743680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 548 (or 514 counting only the distinct ones).

The product of its (nonzero) digits is 6322176, while the sum is 54.

The spelling of 21721724743680 in words is "twenty-one trillion, seven hundred twenty-one billion, seven hundred twenty-four million, seven hundred forty-three thousand, six hundred eighty".