30781 has 2 divisors, whose sum is σ = 30782. Its totient is φ = 30780.

The previous prime is 30773. The next prime is 30803. The reversal of 30781 is 18703.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 22500 + 8281 = 150^2 + 91^2 .

It is a cyclic number.

It is not a de Polignac number, because 30781 - 2³ = 30773 is a prime.

It is a super-2 number, since 2×30781² = 1894939922, which contains 22 as substring.

It is an Ulam number.

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

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (30181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15390 + 15391.

It is an arithmetic number, because the mean of its divisors is an integer number (15391).

2³⁰⁷⁸¹ is an apocalyptic number.

It is an amenable number.

30781 is a deficient number, since it is larger than the sum of its proper divisors (1).

30781 is an equidigital number, since it uses as much as digits as its factorization.

30781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 168, while the sum is 19.

The square root of 30781 is about 175.4451481233. The cubic root of 30781 is about 31.3396571915.

The spelling of 30781 in words is "thirty thousand, seven hundred eighty-one".