21216040 has 16 divisors (see below), whose sum is σ = 47736180. Its totient is φ = 8486400.

The previous prime is 21216011. The next prime is 21216047. The reversal of 21216040 is 4061212.

It can be written as a sum of positive squares in 2 ways, for example, as 21178404 + 37636 = 4602^2 + 194^2 .

It is not an unprimeable number, because it can be changed into a prime (21216047) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 265161 + ... + 265240.

Almost surely, 2^21216040 is an apocalyptic number.

21216040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21216040 is an abundant number, since it is smaller than the sum of its proper divisors (26520140).

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

21216040 is a wasteful number, since it uses less digits than its factorization.

21216040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 530412 (or 530408 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 16.

The square root of 21216040 is about 4606.0872766373. The cubic root of 21216040 is about 276.8352837399.

Adding to 21216040 its reverse (4061212), we get a palindrome (25277252).

The spelling of 21216040 in words is "twenty-one million, two hundred sixteen thousand, forty".