30721 has 4 divisors (see below), whose sum is σ = 31744. Its totient is φ = 29700.

The previous prime is 30713. The next prime is 30727. The reversal of 30721 is 12703.

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 30721 - 2³ = 30713 is a prime.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (30727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 465 + ... + 526.

It is an arithmetic number, because the mean of its divisors is an integer number (7936).

It is a Proth number, since it is equal to 15 ⋅ 2¹¹ + 1 and 15 < 2¹¹.

2³⁰⁷²¹ is an apocalyptic number.

30721 is a gapful number since it is divisible by the number (31) formed by its first and last digit.

It is an amenable number.

30721 is a deficient number, since it is larger than the sum of its proper divisors (1023).

30721 is an equidigital number, since it uses as much as digits as its factorization.

30721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1022.

The product of its (nonzero) digits is 42, while the sum is 13.

The square root of 30721 is about 175.2740711001. The cubic root of 30721 is about 31.3192809579.

The spelling of 30721 in words is "thirty thousand, seven hundred twenty-one".