161217781 has 8 divisors (see below), whose sum is σ = 165443544. Its totient is φ = 157006080.

The previous prime is 161217773. The next prime is 161217809. The reversal of 161217781 is 187712161.

It can be written as a sum of positive squares in 4 ways, for example, as 54756 + 161163025 = 234^2 + 12695^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 161217781 - 2³ = 161217773 is a prime.

It is a super-2 number, since 2×161217781² = 51982345821127922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161217751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 22111 + ... + 28483.

It is an arithmetic number, because the mean of its divisors is an integer number (20680443).

Almost surely, 2^161217781 is an apocalyptic number.

It is an amenable number.

161217781 is a deficient number, since it is larger than the sum of its proper divisors (4225763).

161217781 is an equidigital number, since it uses as much as digits as its factorization.

161217781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7031.

The product of its digits is 4704, while the sum is 34.

The square root of 161217781 is about 12697.1564139377. The cubic root of 161217781 is about 544.2573629504.

The spelling of 161217781 in words is "one hundred sixty-one million, two hundred seventeen thousand, seven hundred eighty-one".