1981997 has 2 divisors, whose sum is σ = 1981998. Its totient is φ = 1981996.

The previous prime is 1981963. The next prime is 1982011. The reversal of 1981997 is 7991891.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1590121 + 391876 = 1261^2 + 626^2 .

It is an emirp because it is prime and its reverse (7991891) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1981997 - 2¹⁸ = 1719853 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1981297) by changing a digit.

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 as a sum of consecutive naturals, namely, 990998 + 990999.

It is an arithmetic number, because the mean of its divisors is an integer number (990999).

2^1981997 is an apocalyptic number.

It is an amenable number.

1981997 is a deficient number, since it is larger than the sum of its proper divisors (1).

1981997 is an equidigital number, since it uses as much as digits as its factorization.

1981997 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 40824, while the sum is 44.

The square root of 1981997 is about 1407.8341521642. The cubic root of 1981997 is about 125.6129256648.

The spelling of 1981997 in words is "one million, nine hundred eighty-one thousand, nine hundred ninety-seven".