21281380 has 12 divisors (see below), whose sum is σ = 44690940. Its totient is φ = 8512544.

The previous prime is 21281369. The next prime is 21281441. The reversal of 21281380 is 8318212.

It can be written as a sum of positive squares in 2 ways, for example, as 5456896 + 15824484 = 2336^2 + 3978^2 .

It is an unprimeable number.

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, 532015 + ... + 532054.

It is an arithmetic number, because the mean of its divisors is an integer number (3724245).

Almost surely, 2^21281380 is an apocalyptic number.

21281380 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21281380 is an abundant number, since it is smaller than the sum of its proper divisors (23409560).

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

21281380 is a wasteful number, since it uses less digits than its factorization.

21281380 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1064078 (or 1064076 counting only the distinct ones).

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

The square root of 21281380 is about 4613.1746119131. The cubic root of 21281380 is about 277.1191865466.

Adding to 21281380 its reverse (8318212), we get a palindrome (29599592).

The spelling of 21281380 in words is "twenty-one million, two hundred eighty-one thousand, three hundred eighty".