1981901 has 2 divisors, whose sum is σ = 1981902. Its totient is φ = 1981900.

The previous prime is 1981891. The next prime is 1981919. The reversal of 1981901 is 1091891.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1267876 + 714025 = 1126^2 + 845^2 .

It is a cyclic number.

It is not a de Polignac number, because 1981901 - 2¹⁰ = 1980877 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1981921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 990950 + 990951.

It is an arithmetic number, because the mean of its divisors is an integer number (990951).

2^1981901 is an apocalyptic number.

It is an amenable number.

1981901 is a deficient number, since it is larger than the sum of its proper divisors (1).

1981901 is an equidigital number, since it uses as much as digits as its factorization.

1981901 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 648, while the sum is 29.

The square root of 1981901 is about 1407.8000568263. The cubic root of 1981901 is about 125.6108975696.

It can be divided in two parts, 1981 and 901, that added together give a palindrome (2882).

The spelling of 1981901 in words is "one million, nine hundred eighty-one thousand, nine hundred one".