1997678591 has 4 divisors (see below), whose sum is σ = 1998054000. Its totient is φ = 1997303184.

The previous prime is 1997678561. The next prime is 1997678621. The reversal of 1997678591 is 1958767991.

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

It is an interprime number because it is at equal distance from previous prime (1997678561) and next prime (1997678621).

It is a cyclic number.

It is not a de Polignac number, because 1997678591 - 2¹⁰ = 1997677567 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 (1997678531) 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, 179606 + ... + 190403.

It is an arithmetic number, because the mean of its divisors is an integer number (499513500).

Almost surely, 2^1997678591 is an apocalyptic number.

1997678591 is a deficient number, since it is larger than the sum of its proper divisors (375409).

1997678591 is an equidigital number, since it uses as much as digits as its factorization.

1997678591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 375408.

The product of its digits is 8573040, while the sum is 62.

The square root of 1997678591 is about 44695.3978727117. The cubic root of 1997678591 is about 1259.4333958280.

The spelling of 1997678591 in words is "one billion, nine hundred ninety-seven million, six hundred seventy-eight thousand, five hundred ninety-one".