161638381 has 2 divisors, whose sum is σ = 161638382. Its totient is φ = 161638380.

The previous prime is 161638369. The next prime is 161638409. The reversal of 161638381 is 183836161.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 89965225 + 71673156 = 9485^2 + 8466^2 .

It is an emirp because it is prime and its reverse (183836161) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 161638381 - 2⁹ = 161637869 is a prime.

It is a super-2 number, since 2×161638381² = 52253932424602322, which contains 22 as substring.

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

It is a self number, because there is not a number n which added to its sum of digits gives 161638381.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161638331) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80819190 + 80819191.

It is an arithmetic number, because the mean of its divisors is an integer number (80819191).

Almost surely, 2^161638381 is an apocalyptic number.

It is an amenable number.

161638381 is a deficient number, since it is larger than the sum of its proper divisors (1).

161638381 is an equidigital number, since it uses as much as digits as its factorization.

161638381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 37.

The square root of 161638381 is about 12713.7083889792. The cubic root of 161638381 is about 544.7302550888.

The spelling of 161638381 in words is "one hundred sixty-one million, six hundred thirty-eight thousand, three hundred eighty-one".