21531315 has 32 divisors (see below), whose sum is σ = 37477440. Its totient is φ = 10492416.

The previous prime is 21531269. The next prime is 21531317. The reversal of 21531315 is 51313512.

It is not a de Polignac number, because 21531315 - 2¹⁰ = 21530291 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21531291 and 21531300.

It is not an unprimeable number, because it can be changed into a prime (21531317) 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 31 ways as a sum of consecutive naturals, for example, 20749 + ... + 21761.

It is an arithmetic number, because the mean of its divisors is an integer number (1171170).

Almost surely, 2^21531315 is an apocalyptic number.

21531315 is a deficient number, since it is larger than the sum of its proper divisors (15946125).

21531315 is a wasteful number, since it uses less digits than its factorization.

21531315 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1143.

The product of its digits is 450, while the sum is 21.

The square root of 21531315 is about 4640.1848023543. The cubic root of 21531315 is about 278.1998244163.

Adding to 21531315 its reverse (51313512), we get a palindrome (72844827).

The spelling of 21531315 in words is "twenty-one million, five hundred thirty-one thousand, three hundred fifteen".