21510856640 has 448 divisors, whose sum is σ = 66240599040. Its totient is φ = 6471843840.

The previous prime is 21510856639. The next prime is 21510856667. The reversal of 21510856640 is 4665801512.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (448).

It is a junction number, because it is equal to n+sod(n) for n = 21510856594 and 21510856603.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 51338351 + ... + 51338769.

It is an arithmetic number, because the mean of its divisors is an integer number (147858480).

Almost surely, 2^21510856640 is an apocalyptic number.

21510856640 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 21510856640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33120299520).

21510856640 is an abundant number, since it is smaller than the sum of its proper divisors (44729742400).

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

21510856640 is a wasteful number, since it uses less digits than its factorization.

21510856640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 540 (or 530 counting only the distinct ones).

The product of its (nonzero) digits is 57600, while the sum is 38.

The spelling of 21510856640 in words is "twenty-one billion, five hundred ten million, eight hundred fifty-six thousand, six hundred forty".