21221517 has 4 divisors (see below), whose sum is σ = 28295360. Its totient is φ = 14147676.

The previous prime is 21221509. The next prime is 21221521. The reversal of 21221517 is 71512212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21221517 - 2³ = 21221509 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21221493 and 21221502.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21221597) 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 3 ways as a sum of consecutive naturals, for example, 3536917 + ... + 3536922.

It is an arithmetic number, because the mean of its divisors is an integer number (7073840).

Almost surely, 2^21221517 is an apocalyptic number.

It is an amenable number.

21221517 is a deficient number, since it is larger than the sum of its proper divisors (7073843).

21221517 is an equidigital number, since it uses as much as digits as its factorization.

21221517 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7073842.

The product of its digits is 280, while the sum is 21.

The square root of 21221517 is about 4606.6817775922. The cubic root of 21221517 is about 276.8591037112.

Adding to 21221517 its reverse (71512212), we get a palindrome (92733729).

The spelling of 21221517 in words is "twenty-one million, two hundred twenty-one thousand, five hundred seventeen".