21005316 has 18 divisors (see below), whose sum is σ = 53096862. Its totient is φ = 7001760.

The previous prime is 21005311. The next prime is 21005329. The reversal of 21005316 is 61350012.

It can be written as a sum of positive squares in only one way, i.e., 20520900 + 484416 = 4530^2 + 696^2 .

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 not an unprimeable number, because it can be changed into a prime (21005311) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 291705 + ... + 291776.

Almost surely, 2^21005316 is an apocalyptic number.

It is an amenable number.

21005316 is an abundant number, since it is smaller than the sum of its proper divisors (32091546).

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

21005316 is a wasteful number, since it uses less digits than its factorization.

21005316 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 583491 (or 583486 counting only the distinct ones).

The product of its (nonzero) digits is 180, while the sum is 18.

The square root of 21005316 is about 4583.1556814056. The cubic root of 21005316 is about 275.9156957389.

Adding to 21005316 its reverse (61350012), we get a palindrome (82355328).

It can be divided in two parts, 21005 and 316, that added together give a triangular number (21321 = T₂₀₆).

The spelling of 21005316 in words is "twenty-one million, five thousand, three hundred sixteen".