21041721 has 16 divisors (see below), whose sum is σ = 32814400. Its totient is φ = 13289184.

The previous prime is 21041719. The next prime is 21041723. The reversal of 21041721 is 12714012.

It is an interprime number because it is at equal distance from previous prime (21041719) and next prime (21041723).

It is not a de Polignac number, because 21041721 - 2¹ = 21041719 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21041694 and 21041703.

It is not an unprimeable number, because it can be changed into a prime (21041723) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19996 + ... + 21021.

It is an arithmetic number, because the mean of its divisors is an integer number (2050900).

Almost surely, 2^21041721 is an apocalyptic number.

It is an amenable number.

21041721 is a deficient number, since it is larger than the sum of its proper divisors (11772679).

21041721 is a wasteful number, since it uses less digits than its factorization.

21041721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41045 (or 41039 counting only the distinct ones).

The product of its (nonzero) digits is 112, while the sum is 18.

The square root of 21041721 is about 4587.1255705507. The cubic root of 21041721 is about 276.0750032454.

Adding to 21041721 its reverse (12714012), we get a palindrome (33755733).

The spelling of 21041721 in words is "twenty-one million, forty-one thousand, seven hundred twenty-one".