1981505 has 4 divisors (see below), whose sum is σ = 2377812. Its totient is φ = 1585200.

The previous prime is 1981493. The next prime is 1981513. The reversal of 1981505 is 5051891.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1073296 + 908209 = 1036^2 + 953^2 .

It is a de Polignac number, because none of the positive numbers 2^k-1981505 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 198146 + ... + 198155.

It is an arithmetic number, because the mean of its divisors is an integer number (594453).

2^1981505 is an apocalyptic number.

It is an amenable number.

1981505 is a deficient number, since it is larger than the sum of its proper divisors (396307).

1981505 is an equidigital number, since it uses as much as digits as its factorization.

1981505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 396306.

The product of its (nonzero) digits is 1800, while the sum is 29.

The square root of 1981505 is about 1407.6594048277. The cubic root of 1981505 is about 125.6025309847.

It can be divided in two parts, 1981 and 505, that multiplied together give a triangular number (1000405 = T₁₄₁₄).

The spelling of 1981505 in words is "one million, nine hundred eighty-one thousand, five hundred five".