21371521 has 8 divisors (see below), whose sum is σ = 22314600. Its totient is φ = 20442240.

The previous prime is 21371509. The next prime is 21371551. The reversal of 21371521 is 12517312.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 8151025 + 13220496 = 2855^2 + 3636^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21371521 - 2⁵ = 21371489 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21371492 and 21371501.

It is not an unprimeable number, because it can be changed into a prime (21371551) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 220 + ... + 6541.

It is an arithmetic number, because the mean of its divisors is an integer number (2789325).

Almost surely, 2^21371521 is an apocalyptic number.

It is an amenable number.

21371521 is a deficient number, since it is larger than the sum of its proper divisors (943079).

21371521 is a wasteful number, since it uses less digits than its factorization.

21371521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6899.

The product of its digits is 420, while the sum is 22.

The square root of 21371521 is about 4622.9342413666. The cubic root of 21371521 is about 277.5098976531.

Adding to 21371521 its reverse (12517312), we get a palindrome (33888833).

The spelling of 21371521 in words is "twenty-one million, three hundred seventy-one thousand, five hundred twenty-one".