1643987 has 2 divisors, whose sum is σ = 1643988. Its totient is φ = 1643986.

The previous prime is 1643969. The next prime is 1643989. The reversal of 1643987 is 7893461.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1643987 - 2¹⁴ = 1627603 is a prime.

Together with 1643989, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1643987.

It is not a weakly prime, because it can be changed into another prime (1643989) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 821993 + 821994.

It is an arithmetic number, because the mean of its divisors is an integer number (821994).

2^1643987 is an apocalyptic number.

1643987 is a deficient number, since it is larger than the sum of its proper divisors (1).

1643987 is an equidigital number, since it uses as much as digits as its factorization.

1643987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 36288, while the sum is 38.

The square root of 1643987 is about 1282.1805645072. The cubic root of 1643987 is about 118.0228577763.

The spelling of 1643987 in words is "one million, six hundred forty-three thousand, nine hundred eighty-seven".