151991 has 4 divisors (see below), whose sum is σ = 173712. Its totient is φ = 130272.

The previous prime is 151969. The next prime is 152003. The reversal of 151991 is 199151.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 151991 - 2¹⁰ = 150967 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 151991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (151901) 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, 10850 + ... + 10863.

It is an arithmetic number, because the mean of its divisors is an integer number (43428).

2¹⁵¹⁹⁹¹ is an apocalyptic number.

151991 is a deficient number, since it is larger than the sum of its proper divisors (21721).

151991 is an equidigital number, since it uses as much as digits as its factorization.

151991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21720.

The product of its digits is 405, while the sum is 26.

The square root of 151991 is about 389.8602313650. The cubic root of 151991 is about 53.3669796372.

The spelling of 151991 in words is "one hundred fifty-one thousand, nine hundred ninety-one".