21312521 has 4 divisors (see below), whose sum is σ = 21475344. Its totient is φ = 21149700.

The previous prime is 21312517. The next prime is 21312523. The reversal of 21312521 is 12521312.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21312521 - 2² = 21312517 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21312521.

It is not an unprimeable number, because it can be changed into a prime (21312523) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 81215 + ... + 81476.

It is an arithmetic number, because the mean of its divisors is an integer number (5368836).

Almost surely, 2^21312521 is an apocalyptic number.

It is an amenable number.

21312521 is a deficient number, since it is larger than the sum of its proper divisors (162823).

21312521 is a wasteful number, since it uses less digits than its factorization.

21312521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 162822.

The product of its digits is 120, while the sum is 17.

The square root of 21312521 is about 4616.5486025818. The cubic root of 21312521 is about 277.2542899828.

Adding to 21312521 its reverse (12521312), we get a palindrome (33833833).

The spelling of 21312521 in words is "twenty-one million, three hundred twelve thousand, five hundred twenty-one".