7215721 has 4 divisors (see below), whose sum is σ = 7529472. Its totient is φ = 6901972.

The previous prime is 7215709. The next prime is 7215739. The reversal of 7215721 is 1275127.

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.

It is a cyclic number.

It is not a de Polignac number, because 7215721 - 2⁹ = 7215209 is a prime.

It is a Duffinian number.

7215721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (7215121) 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, 156841 + ... + 156886.

It is an arithmetic number, because the mean of its divisors is an integer number (1882368).

Almost surely, 2^7215721 is an apocalyptic number.

It is an amenable number.

7215721 is a deficient number, since it is larger than the sum of its proper divisors (313751).

7215721 is a wasteful number, since it uses less digits than its factorization.

7215721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 313750.

The product of its digits is 980, while the sum is 25.

The square root of 7215721 is about 2686.2094110475. The cubic root of 7215721 is about 193.2383160392.

The spelling of 7215721 in words is "seven million, two hundred fifteen thousand, seven hundred twenty-one".