20521721 has 12 divisors (see below), whose sum is σ = 23288832. Its totient is φ = 18051000.

The previous prime is 20521679. The next prime is 20521723. The reversal of 20521721 is 12712502.

It is not a de Polignac number, because 20521721 - 2²² = 16327417 is a prime.

It is a super-2 number, since 2×20521721² = 842282065603682, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20521693 and 20521702.

It is not an unprimeable number, because it can be changed into a prime (20521723) 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 11 ways as a sum of consecutive naturals, for example, 1016 + ... + 6486.

It is an arithmetic number, because the mean of its divisors is an integer number (1940736).

Almost surely, 2^20521721 is an apocalyptic number.

It is an amenable number.

20521721 is a deficient number, since it is larger than the sum of its proper divisors (2767111).

20521721 is a wasteful number, since it uses less digits than its factorization.

20521721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5524 (or 5513 counting only the distinct ones).

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 20521721 is about 4530.0906171952. The cubic root of 20521721 is about 273.7818116670.

It can be divided in two parts, 2052 and 1721, that added together give a palindrome (3773).

The spelling of 20521721 in words is "twenty million, five hundred twenty-one thousand, seven hundred twenty-one".