21651552 has 72 divisors (see below), whose sum is σ = 66319344. Its totient is φ = 6660864.

The previous prime is 21651551. The next prime is 21651559. The reversal of 21651552 is 25515612.

21651552 is a `hidden beast` number, since 2 + 1 + 651 + 5 + 5 + 2 = 666.

It is a tau number, because it is divible by the number of its divisors (72).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651551) 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, 853 + ... + 6635.

It is an arithmetic number, because the mean of its divisors is an integer number (921102).

Almost surely, 2^21651552 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 21651552, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33159672).

21651552 is an abundant number, since it is smaller than the sum of its proper divisors (44667792).

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

21651552 is a wasteful number, since it uses less digits than its factorization.

21651552 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5812 (or 5801 counting only the distinct ones).

The product of its digits is 3000, while the sum is 27.

The square root of 21651552 is about 4653.1228223635. The cubic root of 21651552 is about 278.7167124950.

The spelling of 21651552 in words is "twenty-one million, six hundred fifty-one thousand, five hundred fifty-two".