1721621 has 4 divisors (see below), whose sum is σ = 1878144. Its totient is φ = 1565100.

The previous prime is 1721593. The next prime is 1721633. The reversal of 1721621 is 1261271.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1261271 = 11 ⋅114661.

It is a cyclic number.

It is not a de Polignac number, because 1721621 - 2⁶ = 1721557 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a nialpdrome in base 11.

It is a junction number, because it is equal to n+sod(n) for n = 1721593 and 1721602.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1721651) 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, 78245 + ... + 78266.

It is an arithmetic number, because the mean of its divisors is an integer number (469536).

2^1721621 is an apocalyptic number.

1721621 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1721621 is a deficient number, since it is larger than the sum of its proper divisors (156523).

1721621 is a wasteful number, since it uses less digits than its factorization.

1721621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 156522.

The product of its digits is 168, while the sum is 20.

The square root of 1721621 is about 1312.1055597779. The cubic root of 1721621 is about 119.8521558888.

Adding to 1721621 its reverse (1261271), we get a palindrome (2982892).

The spelling of 1721621 in words is "one million, seven hundred twenty-one thousand, six hundred twenty-one".