1691297987 has 4 divisors (see below), whose sum is σ = 1691700840. Its totient is φ = 1690895136.

The previous prime is 1691297983. The next prime is 1691298019. The reversal of 1691297987 is 7897921961.

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 1691297987 - 2² = 1691297983 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1691297981) 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, 195062 + ... + 203547.

It is an arithmetic number, because the mean of its divisors is an integer number (422925210).

Almost surely, 2^1691297987 is an apocalyptic number.

1691297987 is a deficient number, since it is larger than the sum of its proper divisors (402853).

1691297987 is an equidigital number, since it uses as much as digits as its factorization.

1691297987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 402852.

The product of its digits is 3429216, while the sum is 59.

The square root of 1691297987 is about 41125.3934570844. The cubic root of 1691297987 is about 1191.4432943370.

The spelling of 1691297987 in words is "one billion, six hundred ninety-one million, two hundred ninety-seven thousand, nine hundred eighty-seven".