21531557376 has 640 divisors, whose sum is σ = 76665093120. Its totient is φ = 5912248320.

The previous prime is 21531557357. The next prime is 21531557389. The reversal of 21531557376 is 67375513512.

21531557376 is a `hidden beast` number, since 2 + 1 + 5 + 3 + 1 + 5 + 573 + 76 = 666.

It is a congruent number.

It is an unprimeable number.

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 63 ways as a sum of consecutive naturals, for example, 321366495 + ... + 321366561.

It is an arithmetic number, because the mean of its divisors is an integer number (119789208).

Almost surely, 2^21531557376 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21531557376, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38332546560).

21531557376 is an abundant number, since it is smaller than the sum of its proper divisors (55133535744).

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

21531557376 is an frugal number, since it uses more digits than its factorization.

21531557376 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 154 (or 120 counting only the distinct ones).

The product of its digits is 661500, while the sum is 45.

It can be divided in two parts, 215315 and 57376, that added together give a triangular number (272691 = T₇₃₈).

The spelling of 21531557376 in words is "twenty-one billion, five hundred thirty-one million, five hundred fifty-seven thousand, three hundred seventy-six".