155917991 has 2 divisors, whose sum is σ = 155917992. Its totient is φ = 155917990.

The previous prime is 155917987. The next prime is 155918011. The reversal of 155917991 is 199719551.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 155917991 - 2² = 155917987 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (155917961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 77958995 + 77958996.

It is an arithmetic number, because the mean of its divisors is an integer number (77958996).

Almost surely, 2^155917991 is an apocalyptic number.

155917991 is a deficient number, since it is larger than the sum of its proper divisors (1).

155917991 is an equidigital number, since it uses as much as digits as its factorization.

155917991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 127575, while the sum is 47.

The square root of 155917991 is about 12486.7125777764. The cubic root of 155917991 is about 538.2269130749.

The spelling of 155917991 in words is "one hundred fifty-five million, nine hundred seventeen thousand, nine hundred ninety-one".