21251580 has 48 divisors (see below), whose sum is σ = 68006400. Its totient is φ = 4857408.

The previous prime is 21251543. The next prime is 21251597. The reversal of 21251580 is 8515212.

It is a self number, because there is not a number n which added to its sum of digits gives 21251580.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24880 + ... + 25719.

It is an arithmetic number, because the mean of its divisors is an integer number (1416800).

Almost surely, 2^21251580 is an apocalyptic number.

21251580 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21251580 is an abundant number, since it is smaller than the sum of its proper divisors (46754820).

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

21251580 is a wasteful number, since it uses less digits than its factorization.

21251580 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50618 (or 50616 counting only the distinct ones).

The product of its (nonzero) digits is 800, while the sum is 24.

The square root of 21251580 is about 4609.9436005227. The cubic root of 21251580 is about 276.9897774990.

Adding to 21251580 its reverse (8515212), we get a palindrome (29766792).

The spelling of 21251580 in words is "twenty-one million, two hundred fifty-one thousand, five hundred eighty".