161331781 has 16 divisors (see below), whose sum is σ = 180060160. Its totient is φ = 143544960.

The previous prime is 161331757. The next prime is 161331799. The reversal of 161331781 is 187133161.

It is not a de Polignac number, because 161331781 - 2⁵ = 161331749 is a prime.

It is a super-2 number, since 2×161331781² = 52055887121263922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161331701) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 125500 + ... + 126778.

It is an arithmetic number, because the mean of its divisors is an integer number (11253760).

Almost surely, 2^161331781 is an apocalyptic number.

It is an amenable number.

161331781 is a deficient number, since it is larger than the sum of its proper divisors (18728379).

161331781 is a wasteful number, since it uses less digits than its factorization.

161331781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1636.

The product of its digits is 3024, while the sum is 31.

The square root of 161331781 is about 12701.6448147474. The cubic root of 161331781 is about 544.3856174566.

The spelling of 161331781 in words is "one hundred sixty-one million, three hundred thirty-one thousand, seven hundred eighty-one".