21312173 has 2 divisors, whose sum is σ = 21312174. Its totient is φ = 21312172.

The previous prime is 21312163. The next prime is 21312223. The reversal of 21312173 is 37121312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21141604 + 170569 = 4598^2 + 413^2 .

It is a cyclic number.

It is not a de Polignac number, because 21312173 - 2¹⁶ = 21246637 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21312113) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10656086 + 10656087.

It is an arithmetic number, because the mean of its divisors is an integer number (10656087).

Almost surely, 2^21312173 is an apocalyptic number.

It is an amenable number.

21312173 is a deficient number, since it is larger than the sum of its proper divisors (1).

21312173 is an equidigital number, since it uses as much as digits as its factorization.

21312173 is an evil number, because the sum of its binary digits is even.

The product of its digits is 252, while the sum is 20.

The square root of 21312173 is about 4616.5109119334. The cubic root of 21312173 is about 277.2527809322.

Adding to 21312173 its reverse (37121312), we get a palindrome (58433485).

The spelling of 21312173 in words is "twenty-one million, three hundred twelve thousand, one hundred seventy-three".