20501721 has 16 divisors (see below), whose sum is σ = 30470400. Its totient is φ = 13623984.

The previous prime is 20501699. The next prime is 20501731. The reversal of 20501721 is 12710502.

It is not a de Polignac number, because 20501721 - 2¹¹ = 20499673 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20501694 and 20501703.

It is not an unprimeable number, because it can be changed into a prime (20501731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8875 + ... + 10943.

It is an arithmetic number, because the mean of its divisors is an integer number (1904400).

Almost surely, 2^20501721 is an apocalyptic number.

It is an amenable number.

20501721 is a deficient number, since it is larger than the sum of its proper divisors (9968679).

20501721 is a wasteful number, since it uses less digits than its factorization.

20501721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2445 (or 2439 counting only the distinct ones).

The product of its (nonzero) digits is 140, while the sum is 18.

The square root of 20501721 is about 4527.8826177365. The cubic root of 20501721 is about 273.6928422606.

The spelling of 20501721 in words is "twenty million, five hundred one thousand, seven hundred twenty-one".