1997691 has 4 divisors (see below), whose sum is σ = 2663592. Its totient is φ = 1331792.

The previous prime is 1997683. The next prime is 1997693. The reversal of 1997691 is 1967991.

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 1997691 - 2³ = 1997683 is a prime.

It is a D-number.

1997691 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (1997693) 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, 332946 + ... + 332951.

It is an arithmetic number, because the mean of its divisors is an integer number (665898).

2^1997691 is an apocalyptic number.

1997691 is a deficient number, since it is larger than the sum of its proper divisors (665901).

1997691 is an equidigital number, since it uses as much as digits as its factorization.

1997691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 665900.

The product of its digits is 30618, while the sum is 42.

The square root of 1997691 is about 1413.3969718377. The cubic root of 1997691 is about 125.9436003568.

The spelling of 1997691 in words is "one million, nine hundred ninety-seven thousand, six hundred ninety-one".