1981555 has 4 divisors (see below), whose sum is σ = 2377872. Its totient is φ = 1585240.

The previous prime is 1981547. The next prime is 1981583. The reversal of 1981555 is 5551891.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5551891 = 269 ⋅20639.

It is not a de Polignac number, because 1981555 - 2³ = 1981547 is a prime.

It is a Duffinian number.

It is a zygodrome in base 2.

It is a self number, because there is not a number n which added to its sum of digits gives 1981555.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 198151 + ... + 198160.

It is an arithmetic number, because the mean of its divisors is an integer number (594468).

2^1981555 is an apocalyptic number.

1981555 is a deficient number, since it is larger than the sum of its proper divisors (396317).

1981555 is an equidigital number, since it uses as much as digits as its factorization.

1981555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 396316.

The product of its digits is 9000, while the sum is 34.

The square root of 1981555 is about 1407.6771646937. The cubic root of 1981555 is about 125.6035874332.

The spelling of 1981555 in words is "one million, nine hundred eighty-one thousand, five hundred fifty-five".