159921781 has 4 divisors (see below), whose sum is σ = 161337132. Its totient is φ = 158506432.

The previous prime is 159921779. The next prime is 159921793. The reversal of 159921781 is 187129951.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 51969681 + 107952100 = 7209^2 + 10390^2 .

It is a cyclic number.

It is not a de Polignac number, because 159921781 - 2¹ = 159921779 is a prime.

It is a super-2 number, since 2×159921781² = 51149952076423922, 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 (159921701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 707506 + ... + 707731.

It is an arithmetic number, because the mean of its divisors is an integer number (40334283).

Almost surely, 2^159921781 is an apocalyptic number.

It is an amenable number.

159921781 is a deficient number, since it is larger than the sum of its proper divisors (1415351).

159921781 is a wasteful number, since it uses less digits than its factorization.

159921781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1415350.

The product of its digits is 45360, while the sum is 43.

The square root of 159921781 is about 12646.0183852468. The cubic root of 159921781 is about 542.7950426358.

The spelling of 159921781 in words is "one hundred fifty-nine million, nine hundred twenty-one thousand, seven hundred eighty-one".