1643981 has 8 divisors (see below), whose sum is σ = 1723680. Its totient is φ = 1565872.

The previous prime is 1643969. The next prime is 1643987. The reversal of 1643981 is 1893461.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1643981 - 2¹⁸ = 1381837 is a prime.

It is a super-2 number, since 2×1643981² = 5405347056722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1643987) 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 in 7 ways as a sum of consecutive naturals, for example, 2066 + ... + 2748.

It is an arithmetic number, because the mean of its divisors is an integer number (215460).

2^1643981 is an apocalyptic number.

It is an amenable number.

1643981 is a deficient number, since it is larger than the sum of its proper divisors (79699).

1643981 is an equidigital number, since it uses as much as digits as its factorization.

1643981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 795.

The product of its digits is 5184, while the sum is 32.

The square root of 1643981 is about 1282.1782247410. The cubic root of 1643981 is about 118.0227141949.

The spelling of 1643981 in words is "one million, six hundred forty-three thousand, nine hundred eighty-one".