21388770 has 96 divisors (see below), whose sum is σ = 60815664. Its totient is φ = 5184000.

The previous prime is 21388769. The next prime is 21388777. The reversal of 21388770 is 7788312.

It can be written as a sum of positive squares in 8 ways, for example, as 4422609 + 16966161 = 2103^2 + 4119^2 .

It is a super-2 number, since 2×21388770² = 914958964225800, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21388777) by changing a digit.

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 47 ways as a sum of consecutive naturals, for example, 118080 + ... + 118260.

Almost surely, 2^21388770 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21388770, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30407832).

21388770 is an abundant number, since it is smaller than the sum of its proper divisors (39426894).

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

21388770 is a wasteful number, since it uses less digits than its factorization.

21388770 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 308 (or 305 counting only the distinct ones).

The product of its (nonzero) digits is 18816, while the sum is 36.

The square root of 21388770 is about 4624.7994551115. The cubic root of 21388770 is about 277.5845371854.

The spelling of 21388770 in words is "twenty-one million, three hundred eighty-eight thousand, seven hundred seventy".