21312216 has 96 divisors (see below), whose sum is σ = 61074000. Its totient is φ = 6703872.

The previous prime is 21312173. The next prime is 21312223. The reversal of 21312216 is 61221312.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 123106 + ... + 123278.

Almost surely, 2^21312216 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 21312216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30537000).

21312216 is an abundant number, since it is smaller than the sum of its proper divisors (39761784).

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

21312216 is a wasteful number, since it uses less digits than its factorization.

21312216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 273 (or 266 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21312216 is about 4616.5155691279. The cubic root of 21312216 is about 277.2529673963.

Adding to 21312216 its reverse (61221312), we get a palindrome (82533528).

It can be divided in two parts, 21312 and 216, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 21312216 in words is "twenty-one million, three hundred twelve thousand, two hundred sixteen".