21531216 has 40 divisors (see below), whose sum is σ = 63569344. Its totient is φ = 6151680.

The previous prime is 21531193. The next prime is 21531233. The reversal of 21531216 is 61213512.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a junction number, because it is equal to n+sod(n) for n = 21531192 and 21531201.

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, 31705 + ... + 32376.

Almost surely, 2^21531216 is an apocalyptic number.

It is an amenable number.

21531216 is an abundant number, since it is smaller than the sum of its proper divisors (42038128).

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

21531216 is a wasteful number, since it uses less digits than its factorization.

21531216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 64099 (or 64093 counting only the distinct ones).

The product of its digits is 360, while the sum is 21.

The square root of 21531216 is about 4640.1741346635. The cubic root of 21531216 is about 278.1993980323.

Adding to 21531216 its reverse (61213512), we get a palindrome (82744728).

The spelling of 21531216 in words is "twenty-one million, five hundred thirty-one thousand, two hundred sixteen".