21320517 has 16 divisors (see below), whose sum is σ = 29835648. Its totient is φ = 13516800.

The previous prime is 21320513. The next prime is 21320531. The reversal of 21320517 is 71502312.

It is not a de Polignac number, because 21320517 - 2² = 21320513 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21320493 and 21320502.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21320513) 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 15 ways as a sum of consecutive naturals, for example, 12517 + ... + 14117.

It is an arithmetic number, because the mean of its divisors is an integer number (1864728).

Almost surely, 2^21320517 is an apocalyptic number.

It is an amenable number.

21320517 is a deficient number, since it is larger than the sum of its proper divisors (8515131).

21320517 is a wasteful number, since it uses less digits than its factorization.

21320517 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1820.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21320517 is about 4617.4145362963. The cubic root of 21320517 is about 277.2889589319.

Adding to 21320517 its reverse (71502312), we get a palindrome (92822829).

The spelling of 21320517 in words is "twenty-one million, three hundred twenty thousand, five hundred seventeen".