21252581 has 8 divisors (see below), whose sum is σ = 24416064. Its totient is φ = 18120960.

The previous prime is 21252571. The next prime is 21252589. The reversal of 21252581 is 18525212.

21252581 = 14² + 15² + ... + 399².

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21252581 is a prime.

It is a super-2 number, since 2×21252581² = 903344398323122, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21252581.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21252589) 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 7 ways as a sum of consecutive naturals, for example, 6515 + ... + 9216.

It is an arithmetic number, because the mean of its divisors is an integer number (3052008).

Almost surely, 2^21252581 is an apocalyptic number.

It is an amenable number.

21252581 is a deficient number, since it is larger than the sum of its proper divisors (3163483).

21252581 is a wasteful number, since it uses less digits than its factorization.

21252581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15931.

The product of its digits is 1600, while the sum is 26.

The square root of 21252581 is about 4610.0521689022. The cubic root of 21252581 is about 276.9941263900.

Adding to 21252581 its reverse (18525212), we get a palindrome (39777793).

The spelling of 21252581 in words is "twenty-one million, two hundred fifty-two thousand, five hundred eighty-one".