1997117991 has 64 divisors (see below), whose sum is σ = 3477012480. Its totient is φ = 1120284000.

The previous prime is 1997117971. The next prime is 1997118001.

1997117991 is nontrivially palindromic in base 10.

It is not a de Polignac number, because 1997117991 - 2¹⁷ = 1996986919 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1997117921) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 207046 + ... + 216476.

It is an arithmetic number, because the mean of its divisors is an integer number (54328320).

Almost surely, 2^1997117991 is an apocalyptic number.

1997117991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

1997117991 is a deficient number, since it is larger than the sum of its proper divisors (1479894489).

1997117991 is a wasteful number, since it uses less digits than its factorization.

1997117991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9505 (or 9499 counting only the distinct ones).

The product of its digits is 321489, while the sum is 54.

The square root of 1997117991 is about 44689.1260934917. The cubic root of 1997117991 is about 1259.3155750035.

It can be divided in two parts, 199711 and 7991, that added together give a palindrome (207702).

The spelling of 1997117991 in words is "one billion, nine hundred ninety-seven million, one hundred seventeen thousand, nine hundred ninety-one".