21221316 has 18 divisors (see below), whose sum is σ = 53642862. Its totient is φ = 7073760.

The previous prime is 21221303. The next prime is 21221339. The reversal of 21221316 is 61312212.

It can be written as a sum of positive squares in only one way, i.e., 20793600 + 427716 = 4560^2 + 654^2 .

It is a tau number, because it is divible by the number of its divisors (18).

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 an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 294705 + ... + 294776.

It is an arithmetic number, because the mean of its divisors is an integer number (2980159).

Almost surely, 2^21221316 is an apocalyptic number.

It is an amenable number.

21221316 is an abundant number, since it is smaller than the sum of its proper divisors (32421546).

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

21221316 is a wasteful number, since it uses less digits than its factorization.

21221316 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 589491 (or 589486 counting only the distinct ones).

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

The square root of 21221316 is about 4606.6599614037. The cubic root of 21221316 is about 276.8582296164.

Adding to 21221316 its reverse (61312212), we get a palindrome (82533528).

It can be divided in two parts, 212 and 21316, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 21221316 in words is "twenty-one million, two hundred twenty-one thousand, three hundred sixteen".