21215640 has 32 divisors (see below), whose sum is σ = 63647280. Its totient is φ = 5657472.

The previous prime is 21215627. The next prime is 21215657. The reversal of 21215640 is 4651212.

It is a congruent number.

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, 88279 + ... + 88518.

Almost surely, 2^21215640 is an apocalyptic number.

21215640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21215640 is an abundant number, since it is smaller than the sum of its proper divisors (42431640).

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

21215640 is a wasteful number, since it uses less digits than its factorization.

21215640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 176811 (or 176807 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 21215640 is about 4606.0438556314. The cubic root of 21215640 is about 276.8335439429.

Adding to 21215640 its reverse (4651212), we get a palindrome (25866852).

The spelling of 21215640 in words is "twenty-one million, two hundred fifteen thousand, six hundred forty".