1981615 has 4 divisors (see below), whose sum is σ = 2377944. Its totient is φ = 1585288.

The previous prime is 1981607. The next prime is 1981619. The reversal of 1981615 is 5161891.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5161891 = 7 ⋅737413.

It is a cyclic number.

It is not a de Polignac number, because 1981615 - 2³ = 1981607 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1981619) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 198157 + ... + 198166.

It is an arithmetic number, because the mean of its divisors is an integer number (594486).

2^1981615 is an apocalyptic number.

1981615 is a deficient number, since it is larger than the sum of its proper divisors (396329).

1981615 is an equidigital number, since it uses as much as digits as its factorization.

1981615 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 396328.

The product of its digits is 2160, while the sum is 31.

The square root of 1981615 is about 1407.6984762370. The cubic root of 1981615 is about 125.6048551479.

The spelling of 1981615 in words is "one million, nine hundred eighty-one thousand, six hundred fifteen".