7218921 has 4 divisors (see below), whose sum is σ = 9625232. Its totient is φ = 4812612.

The previous prime is 7218919. The next prime is 7218929. The reversal of 7218921 is 1298127.

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 not a de Polignac number, because 7218921 - 2¹ = 7218919 is a prime.

It is a super-2 number, since 2×7218921² = 104225640808482, which contains 22 as substring.

It is an alternating number because its digits alternate between odd and even.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (7218929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1203151 + ... + 1203156.

It is an arithmetic number, because the mean of its divisors is an integer number (2406308).

Almost surely, 2^7218921 is an apocalyptic number.

It is an amenable number.

7218921 is a deficient number, since it is larger than the sum of its proper divisors (2406311).

7218921 is a wasteful number, since it uses less digits than its factorization.

7218921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2406310.

The product of its digits is 2016, while the sum is 30.

The square root of 7218921 is about 2686.8049798971. The cubic root of 7218921 is about 193.2668773441.

The spelling of 7218921 in words is "seven million, two hundred eighteen thousand, nine hundred twenty-one".