381856561 has 2 divisors, whose sum is σ = 381856562. Its totient is φ = 381856560.

The previous prime is 381856549. The next prime is 381856577. The reversal of 381856561 is 165658183.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 229704336 + 152152225 = 15156^2 + 12335^2 .

It is a cyclic number.

It is not a de Polignac number, because 381856561 - 2⁹ = 381856049 is a prime.

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

It is not a weakly prime, because it can be changed into another prime (381853561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 190928280 + 190928281.

It is an arithmetic number, because the mean of its divisors is an integer number (190928281).

Almost surely, 2^381856561 is an apocalyptic number.

It is an amenable number.

381856561 is a deficient number, since it is larger than the sum of its proper divisors (1).

381856561 is an equidigital number, since it uses as much as digits as its factorization.

381856561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 172800, while the sum is 43.

The square root of 381856561 is about 19541.1504523147. The cubic root of 381856561 is about 725.4933216383.

The spelling of 381856561 in words is "three hundred eighty-one million, eight hundred fifty-six thousand, five hundred sixty-one".