21399552 has 144 divisors (see below), whose sum is σ = 65585520. Its totient is φ = 6967296.

The previous prime is 21399551. The next prime is 21399559. The reversal of 21399552 is 25599312.

21399552 = 33³ + 34³ + ... + 96³.

It is a happy number.

21399552 is a `hidden beast` number, since 2 + 13 + 99 + 552 = 666.

It is a tau number, because it is divible by the number of its divisors (144).

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

It is a nialpdrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (21399551) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 497643 + ... + 497685.

It is an arithmetic number, because the mean of its divisors is an integer number (455455).

Almost surely, 2^21399552 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 21399552, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32792760).

21399552 is an abundant number, since it is smaller than the sum of its proper divisors (44185968).

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

21399552 is an frugal number, since it uses more digits than its factorization.

21399552 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80 (or 48 counting only the distinct ones).

The product of its digits is 24300, while the sum is 36.

The square root of 21399552 is about 4625.9649804122. The cubic root of 21399552 is about 277.6311724636.

The spelling of 21399552 in words is "twenty-one million, three hundred ninety-nine thousand, five hundred fifty-two".