21210388 has 12 divisors (see below), whose sum is σ = 37818900. Its totient is φ = 10404992.

The previous prime is 21210379. The next prime is 21210389. The reversal of 21210388 is 88301212.

It can be written as a sum of positive squares in 2 ways, for example, as 5702544 + 15507844 = 2388^2 + 3938^2 .

It is a super-2 number, since 2×21210388² = 899761118221088, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21210389) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 49813 + ... + 50236.

It is an arithmetic number, because the mean of its divisors is an integer number (3151575).

Almost surely, 2^21210388 is an apocalyptic number.

It is an amenable number.

21210388 is a deficient number, since it is larger than the sum of its proper divisors (16608512).

21210388 is a wasteful number, since it uses less digits than its factorization.

21210388 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 100106 (or 100104 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 25.

The square root of 21210388 is about 4605.4736998489. The cubic root of 21210388 is about 276.8106983792.

It can be divided in two parts, 212 and 10388, that multiplied together give a square (2202256 = 1484²).

The spelling of 21210388 in words is "twenty-one million, two hundred ten thousand, three hundred eighty-eight".