21501380 has 12 divisors (see below), whose sum is σ = 45152940. Its totient is φ = 8600544.

The previous prime is 21501377. The next prime is 21501401. The reversal of 21501380 is 8310512.

It can be written as a sum of positive squares in 2 ways, for example, as 16128256 + 5373124 = 4016^2 + 2318^2 .

It is a Harshad number since it is a multiple of its sum of digits (20), and also a Moran number because the ratio is a prime number: 1075069 = 21501380 / (2 + 1 + 5 + 0 + 1 + 3 + 8 + 0).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 537515 + ... + 537554.

It is an arithmetic number, because the mean of its divisors is an integer number (3762745).

Almost surely, 2^21501380 is an apocalyptic number.

21501380 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21501380 is an abundant number, since it is smaller than the sum of its proper divisors (23651560).

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

21501380 is a wasteful number, since it uses less digits than its factorization.

21501380 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1075078 (or 1075076 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 20.

The square root of 21501380 is about 4636.9580545871. The cubic root of 21501380 is about 278.0708374941.

Adding to 21501380 its reverse (8310512), we get a palindrome (29811892).

The spelling of 21501380 in words is "twenty-one million, five hundred one thousand, three hundred eighty".