21531555440 has 40 divisors (see below), whose sum is σ = 52695652560. Its totient is φ = 8159325696.

The previous prime is 21531555391. The next prime is 21531555443. The reversal of 21531555440 is 4455513512.

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 21531555440.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531555443) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7081229 + ... + 7084268.

It is an arithmetic number, because the mean of its divisors is an integer number (1317391314).

Almost surely, 2^21531555440 is an apocalyptic number.

21531555440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21531555440 is an abundant number, since it is smaller than the sum of its proper divisors (31164097120).

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

21531555440 is a wasteful number, since it uses less digits than its factorization.

21531555440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14165529 (or 14165523 counting only the distinct ones).

The product of its (nonzero) digits is 60000, while the sum is 35.

The spelling of 21531555440 in words is "twenty-one billion, five hundred thirty-one million, five hundred fifty-five thousand, four hundred forty".