215721 has 12 divisors (see below), whose sum is σ = 340080. Its totient is φ = 130680.

The previous prime is 215693. The next prime is 215723. The reversal of 215721 is 127512.

215721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 215721 - 2⁵ = 215689 is a prime.

It is a plaindrome in base 14.

It is a junction number, because it is equal to n+sod(n) for n = 215694 and 215703.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 215721.

It is not an unprimeable number, because it can be changed into a prime (215723) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 991 + ... + 1188.

It is an arithmetic number, because the mean of its divisors is an integer number (28340).

2²¹⁵⁷²¹ is an apocalyptic number.

It is an amenable number.

215721 is a deficient number, since it is larger than the sum of its proper divisors (124359).

215721 is a wasteful number, since it uses less digits than its factorization.

215721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2196 (or 2193 counting only the distinct ones).

The product of its digits is 140, while the sum is 18.

The square root of 215721 is about 464.4577483475. The cubic root of 215721 is about 59.9741555360.

Subtracting from 215721 its reverse (127512), we obtain a square (88209 = 297²).

The spelling of 215721 in words is "two hundred fifteen thousand, seven hundred twenty-one".