21217213 has 8 divisors (see below), whose sum is σ = 21837816. Its totient is φ = 20601600.

The previous prime is 21217199. The next prime is 21217223. The reversal of 21217213 is 31271212.

It can be written as a sum of positive squares in 4 ways, for example, as 38809 + 21178404 = 197^2 + 4602^2 .

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 21217213 - 2¹³ = 21209021 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21217223) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8443 + ... + 10663.

It is an arithmetic number, because the mean of its divisors is an integer number (2729727).

Almost surely, 2^21217213 is an apocalyptic number.

It is an amenable number.

21217213 is a deficient number, since it is larger than the sum of its proper divisors (620603).

21217213 is a wasteful number, since it uses less digits than its factorization.

21217213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2495.

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

The square root of 21217213 is about 4606.2146063769. The cubic root of 21217213 is about 276.8403855686.

Adding to 21217213 its reverse (31271212), we get a palindrome (52488425).

The spelling of 21217213 in words is "twenty-one million, two hundred seventeen thousand, two hundred thirteen".