1021721 has 4 divisors (see below), whose sum is σ = 1023744. Its totient is φ = 1019700.

The previous prime is 1021711. The next prime is 1021747. The reversal of 1021721 is 1271201.

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 a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1021721 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1021696 and 1021705.

It is not an unprimeable number, because it can be changed into a prime (1021711) 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, 476 + ... + 1506.

It is an arithmetic number, because the mean of its divisors is an integer number (255936).

2^1021721 is an apocalyptic number.

It is an amenable number.

1021721 is a deficient number, since it is larger than the sum of its proper divisors (2023).

1021721 is an equidigital number, since it uses as much as digits as its factorization.

1021721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2022.

The product of its (nonzero) digits is 28, while the sum is 14.

The square root of 1021721 is about 1010.8021567053. The cubic root of 1021721 is about 100.7188534483.

Adding to 1021721 its sum of digits (14), we get a triangular number (1021735 = T₁₄₂₉).

Adding to 1021721 its reverse (1271201), we get a palindrome (2292922).

The spelling of 1021721 in words is "one million, twenty-one thousand, seven hundred twenty-one".