155511991 has 2 divisors, whose sum is σ = 155511992. Its totient is φ = 155511990.

The previous prime is 155511959. The next prime is 155512001. The reversal of 155511991 is 199115551.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 155511991 - 2⁵ = 155511959 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 155511991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (155511931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 77755995 + 77755996.

It is an arithmetic number, because the mean of its divisors is an integer number (77755996).

Almost surely, 2^155511991 is an apocalyptic number.

155511991 is a deficient number, since it is larger than the sum of its proper divisors (1).

155511991 is an equidigital number, since it uses as much as digits as its factorization.

155511991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10125, while the sum is 37.

The square root of 155511991 is about 12470.4446993682. Note that the first 3 decimals coincide. The cubic root of 155511991 is about 537.7593380573.

The spelling of 155511991 in words is "one hundred fifty-five million, five hundred eleven thousand, nine hundred ninety-one".