21028551264 has 288 divisors, whose sum is σ = 74607886080. Its totient is φ = 5691658752.

The previous prime is 21028551239. The next prime is 21028551281. The reversal of 21028551264 is 46215582012.

21028551264 is a `hidden beast` number, since 2 + 1 + 0 + 2 + 85 + 512 + 64 = 666.

It is a tau number, because it is divible by the number of its divisors (288).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1024042 + ... + 1044374.

It is an arithmetic number, because the mean of its divisors is an integer number (259055160).

Almost surely, 2^21028551264 is an apocalyptic number.

21028551264 is a gapful number since it is divisible by the number (24) 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 21028551264, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37303943040).

21028551264 is an abundant number, since it is smaller than the sum of its proper divisors (53579334816).

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

21028551264 is a wasteful number, since it uses less digits than its factorization.

21028551264 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20384 (or 20364 counting only the distinct ones).

The product of its (nonzero) digits is 38400, while the sum is 36.

The spelling of 21028551264 in words is "twenty-one billion, twenty-eight million, five hundred fifty-one thousand, two hundred sixty-four".