21217345 has 4 divisors (see below), whose sum is σ = 25460820. Its totient is φ = 16973872.

The previous prime is 21217337. The next prime is 21217367. The reversal of 21217345 is 54371212.

It is a happy number.

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 2286144 + 18931201 = 1512^2 + 4351^2 .

It is a cyclic number.

It is not a de Polignac number, because 21217345 - 2³ = 21217337 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2121730 + ... + 2121739.

It is an arithmetic number, because the mean of its divisors is an integer number (6365205).

Almost surely, 2^21217345 is an apocalyptic number.

It is an amenable number.

21217345 is a deficient number, since it is larger than the sum of its proper divisors (4243475).

21217345 is an equidigital number, since it uses as much as digits as its factorization.

21217345 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4243474.

The product of its digits is 1680, while the sum is 25.

The square root of 21217345 is about 4606.2289348229. The cubic root of 21217345 is about 276.8409596756.

Adding to 21217345 its reverse (54371212), we get a palindrome (75588557).

The spelling of 21217345 in words is "twenty-one million, two hundred seventeen thousand, three hundred forty-five".