721705211021 has 4 divisors (see below), whose sum is σ = 721718209152. Its totient is φ = 721692212892.

The previous prime is 721705210999. The next prime is 721705211057. The reversal of 721705211021 is 120112507127.

It is a happy number.

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: 120112507127 = 5441 ⋅22075447.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-721705211021 is a prime.

It is a super-2 number, since 2×721705211021² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721705211321) 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, 6415421 + ... + 6526946.

It is an arithmetic number, because the mean of its divisors is an integer number (180429552288).

Almost surely, 2^721705211021 is an apocalyptic number.

It is an amenable number.

721705211021 is a deficient number, since it is larger than the sum of its proper divisors (12998131).

721705211021 is a wasteful number, since it uses less digits than its factorization.

721705211021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12998130.

The product of its (nonzero) digits is 1960, while the sum is 29.

Adding to 721705211021 its reverse (120112507127), we get a palindrome (841817718148).

The spelling of 721705211021 in words is "seven hundred twenty-one billion, seven hundred five million, two hundred eleven thousand, twenty-one".