21003552 has 72 divisors (see below), whose sum is σ = 60176844. Its totient is φ = 6948864.

The previous prime is 21003547. The next prime is 21003553. The reversal of 21003552 is 25530012.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 15968016 + 5035536 = 3996^2 + 2244^2 .

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

It is a super-2 number, since 2×21003552² = 882298393233408, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21003553) 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, 66948 + ... + 67260.

Almost surely, 2^21003552 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 21003552, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30088422).

21003552 is an abundant number, since it is smaller than the sum of its proper divisors (39173292).

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

21003552 is a wasteful number, since it uses less digits than its factorization.

21003552 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 562 (or 551 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 21003552 is about 4582.9632335422. The cubic root of 21003552 is about 275.9079718384.

Adding to 21003552 its reverse (25530012), we get a palindrome (46533564).

The spelling of 21003552 in words is "twenty-one million, three thousand, five hundred fifty-two".