21312217 has 4 divisors (see below), whose sum is σ = 21375796. Its totient is φ = 21248640.

The previous prime is 21312173. The next prime is 21312223. The reversal of 21312217 is 71221312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6031936 + 15280281 = 2456^2 + 3909^2 .

It is a cyclic number.

It is not a de Polignac number, because 21312217 - 2²³ = 12923609 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21312194 and 21312203.

It is not an unprimeable number, because it can be changed into a prime (21312257) 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, 31284 + ... + 31957.

It is an arithmetic number, because the mean of its divisors is an integer number (5343949).

Almost surely, 2^21312217 is an apocalyptic number.

It is an amenable number.

21312217 is a deficient number, since it is larger than the sum of its proper divisors (63579).

21312217 is an equidigital number, since it uses as much as digits as its factorization.

21312217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 63578.

The product of its digits is 168, while the sum is 19.

The square root of 21312217 is about 4616.5156774347. The cubic root of 21312217 is about 277.2529717326.

Adding to 21312217 its reverse (71221312), we get a palindrome (92533529).

The spelling of 21312217 in words is "twenty-one million, three hundred twelve thousand, two hundred seventeen".