21523240 has 32 divisors (see below), whose sum is σ = 49226760. Its totient is φ = 8467200.

The previous prime is 21523171. The next prime is 21523261. The reversal of 21523240 is 4232512.

It can be written as a sum of positive squares in 4 ways, for example, as 12630916 + 8892324 = 3554^2 + 2982^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1971 + ... + 6850.

Almost surely, 2^21523240 is an apocalyptic number.

21523240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21523240 is an abundant number, since it is smaller than the sum of its proper divisors (27703520).

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

21523240 is a wasteful number, since it uses less digits than its factorization.

21523240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8893 (or 8889 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 19.

The square root of 21523240 is about 4639.3146045510. The cubic root of 21523240 is about 278.1650418299.

Adding to 21523240 its reverse (4232512), we get a palindrome (25755752).

The spelling of 21523240 in words is "twenty-one million, five hundred twenty-three thousand, two hundred forty".