181921861 has 4 divisors (see below), whose sum is σ = 198460224. Its totient is φ = 165383500.

The previous prime is 181921853. The next prime is 181921877. The reversal of 181921861 is 168129181.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 168129181 = 11 ⋅15284471.

It is a cyclic number.

It is not a de Polignac number, because 181921861 - 2³ = 181921853 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 181921861.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (181921801) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8269165 + ... + 8269186.

It is an arithmetic number, because the mean of its divisors is an integer number (49615056).

Almost surely, 2^181921861 is an apocalyptic number.

181921861 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

181921861 is a deficient number, since it is larger than the sum of its proper divisors (16538363).

181921861 is a wasteful number, since it uses less digits than its factorization.

181921861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16538362.

The product of its digits is 6912, while the sum is 37.

The square root of 181921861 is about 13487.8412283063. The cubic root of 181921861 is about 566.6239970562.

The spelling of 181921861 in words is "one hundred eighty-one million, nine hundred twenty-one thousand, eight hundred sixty-one".