2101661 has 4 divisors (see below), whose sum is σ = 2106300. Its totient is φ = 2097024.

The previous prime is 2101657. The next prime is 2101667. The reversal of 2101661 is 1661012.

It is a happy number.

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 1452025 + 649636 = 1205^2 + 806^2 .

It is a cyclic number.

It is not a de Polignac number, because 2101661 - 2² = 2101657 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 (2101667) 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, 1556 + ... + 2573.

It is an arithmetic number, because the mean of its divisors is an integer number (526575).

2^2101661 is an apocalyptic number.

It is an amenable number.

2101661 is a deficient number, since it is larger than the sum of its proper divisors (4639).

2101661 is an equidigital number, since it uses as much as digits as its factorization.

2101661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4638.

The product of its (nonzero) digits is 72, while the sum is 17.

The square root of 2101661 is about 1449.7106607872. The cubic root of 2101661 is about 128.0916701724.

Adding to 2101661 its reverse (1661012), we get a palindrome (3762673).

The spelling of 2101661 in words is "two million, one hundred one thousand, six hundred sixty-one".