21309380 has 12 divisors (see below), whose sum is σ = 44749740. Its totient is φ = 8523744.

The previous prime is 21309341. The next prime is 21309383. The reversal of 21309380 is 8390312.

It can be written as a sum of positive squares in 2 ways, for example, as 13060996 + 8248384 = 3614^2 + 2872^2 .

It is not an unprimeable number, because it can be changed into a prime (21309383) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 532715 + ... + 532754.

It is an arithmetic number, because the mean of its divisors is an integer number (3729145).

Almost surely, 2^21309380 is an apocalyptic number.

21309380 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21309380 is an abundant number, since it is smaller than the sum of its proper divisors (23440360).

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

21309380 is a wasteful number, since it uses less digits than its factorization.

21309380 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1065478 (or 1065476 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 26.

The square root of 21309380 is about 4616.2084008415. The cubic root of 21309380 is about 277.2406689052.

Adding to 21309380 its reverse (8390312), we get a palindrome (29699692).

The spelling of 21309380 in words is "twenty-one million, three hundred nine thousand, three hundred eighty".