6921721221 has 4 divisors (see below), whose sum is σ = 9228961632. Its totient is φ = 4614480812.

The previous prime is 6921721153. The next prime is 6921721237. The reversal of 6921721221 is 1221271296.

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 not a de Polignac number, because 6921721221 - 2⁹ = 6921720709 is a prime.

It is a super-2 number, since 2×6921721221² = 95820449322483461682, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6921721271) 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, 1153620201 + ... + 1153620206.

It is an arithmetic number, because the mean of its divisors is an integer number (2307240408).

Almost surely, 2^6921721221 is an apocalyptic number.

It is an amenable number.

6921721221 is a deficient number, since it is larger than the sum of its proper divisors (2307240411).

6921721221 is a wasteful number, since it uses less digits than its factorization.

6921721221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2307240410.

The product of its digits is 6048, while the sum is 33.

The square root of 6921721221 is about 83196.8822793258. The cubic root of 6921721221 is about 1905.7738692875.

The spelling of 6921721221 in words is "six billion, nine hundred twenty-one million, seven hundred twenty-one thousand, two hundred twenty-one".