20721117 has 4 divisors (see below), whose sum is σ = 27628160. Its totient is φ = 13814076.

The previous prime is 20721101. The next prime is 20721131. The reversal of 20721117 is 71112702.

It is a happy number.

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 20721117 - 2⁴ = 20721101 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20721093 and 20721102.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20721817) 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, 3453517 + ... + 3453522.

It is an arithmetic number, because the mean of its divisors is an integer number (6907040).

Almost surely, 2^20721117 is an apocalyptic number.

It is an amenable number.

20721117 is a deficient number, since it is larger than the sum of its proper divisors (6907043).

20721117 is an equidigital number, since it uses as much as digits as its factorization.

20721117 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6907042.

The product of its (nonzero) digits is 196, while the sum is 21.

The square root of 20721117 is about 4552.0453644488. The cubic root of 20721117 is about 274.6656741554.

Adding to 20721117 its reverse (71112702), we get a palindrome (91833819).

The spelling of 20721117 in words is "twenty million, seven hundred twenty-one thousand, one hundred seventeen".