1721281621 has 4 divisors (see below), whose sum is σ = 1721948544. Its totient is φ = 1720614700.

The previous prime is 1721281577. The next prime is 1721281633. The reversal of 1721281621 is 1261821271.

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: 1261821271 = 643 ⋅1962397.

It is a cyclic number.

It is not a de Polignac number, because 1721281621 - 2¹³ = 1721273429 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1721281651) 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, 329575 + ... + 334756.

It is an arithmetic number, because the mean of its divisors is an integer number (430487136).

Almost surely, 2^1721281621 is an apocalyptic number.

It is an amenable number.

1721281621 is a deficient number, since it is larger than the sum of its proper divisors (666923).

1721281621 is an equidigital number, since it uses as much as digits as its factorization.

1721281621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 666922.

The product of its digits is 2688, while the sum is 31.

The square root of 1721281621 is about 41488.3311426237. The cubic root of 1721281621 is about 1198.4427998230.

The spelling of 1721281621 in words is "one billion, seven hundred twenty-one million, two hundred eighty-one thousand, six hundred twenty-one".