1981661 has 8 divisors (see below), whose sum is σ = 2208384. Its totient is φ = 1762720.

The previous prime is 1981649. The next prime is 1981663. The reversal of 1981661 is 1661891.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1981661 - 2⁶ = 1981597 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1981663) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1400 + ... + 2433.

It is an arithmetic number, because the mean of its divisors is an integer number (276048).

2^1981661 is an apocalyptic number.

1981661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1981661 is a deficient number, since it is larger than the sum of its proper divisors (226723).

1981661 is a wasteful number, since it uses less digits than its factorization.

1981661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3891.

The product of its digits is 2592, while the sum is 32.

The square root of 1981661 is about 1407.7148148684. The cubic root of 1981661 is about 125.6058270452.

The spelling of 1981661 in words is "one million, nine hundred eighty-one thousand, six hundred sixty-one".