21520304 has 40 divisors (see below), whose sum is σ = 45257520. Its totient is φ = 9854208.

The previous prime is 21520297. The next prime is 21520307. The reversal of 21520304 is 40302512.

It is not an unprimeable number, because it can be changed into a prime (21520307) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 32327 + ... + 32985.

It is an arithmetic number, because the mean of its divisors is an integer number (1131438).

Almost surely, 2^21520304 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 21520304, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22628760).

21520304 is an abundant number, since it is smaller than the sum of its proper divisors (23737216).

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

21520304 is a wasteful number, since it uses less digits than its factorization.

21520304 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 837 (or 831 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 17.

The square root of 21520304 is about 4638.9981677082. The cubic root of 21520304 is about 278.1523930264.

Adding to 21520304 its sum of digits (17), we get a square (21520321 = 4639²).

Adding to 21520304 its reverse (40302512), we get a palindrome (61822816).

The spelling of 21520304 in words is "twenty-one million, five hundred twenty thousand, three hundred four".