21261378528 has 384 divisors, whose sum is σ = 69115213440. Its totient is φ = 6317015040.

The previous prime is 21261378431. The next prime is 21261378557. The reversal of 21261378528 is 82587316212.

21261378528 is a `hidden beast` number, since 2 + 1 + 2 + 613 + 7 + 8 + 5 + 28 = 666.

It is a super-3 number, since 3×21261378528³ (a number of 32 digits) contains 333 as substring.

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, 63089976 + ... + 63090312.

It is an arithmetic number, because the mean of its divisors is an integer number (179987535).

Almost surely, 2^21261378528 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 21261378528, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34557606720).

21261378528 is an abundant number, since it is smaller than the sum of its proper divisors (47853834912).

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

21261378528 is a wasteful number, since it uses less digits than its factorization.

21261378528 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 547 (or 533 counting only the distinct ones).

The product of its digits is 322560, while the sum is 45.

The spelling of 21261378528 in words is "twenty-one billion, two hundred sixty-one million, three hundred seventy-eight thousand, five hundred twenty-eight".