1978123591 has 4 divisors (see below), whose sum is σ = 1978795512. Its totient is φ = 1977451672.

The previous prime is 1978123577. The next prime is 1978123601. The reversal of 1978123591 is 1953218791.

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 1978123591 - 2¹⁷ = 1977992519 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1978123531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 331525 + ... + 337438.

It is an arithmetic number, because the mean of its divisors is an integer number (494698878).

Almost surely, 2^1978123591 is an apocalyptic number.

1978123591 is a deficient number, since it is larger than the sum of its proper divisors (671921).

1978123591 is an equidigital number, since it uses as much as digits as its factorization.

1978123591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 671920.

The product of its digits is 136080, while the sum is 46.

The square root of 1978123591 is about 44476.1013466783. The cubic root of 1978123591 is about 1255.3104401783.

The spelling of 1978123591 in words is "one billion, nine hundred seventy-eight million, one hundred twenty-three thousand, five hundred ninety-one".