2021601661 has 2 divisors, whose sum is σ = 2021601662. Its totient is φ = 2021601660.

The previous prime is 2021601649. The next prime is 2021601709. The reversal of 2021601661 is 1661061202.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 2020952025 + 649636 = 44955^2 + 806^2 .

It is a cyclic number.

It is not a de Polignac number, because 2021601661 - 2¹⁵ = 2021568893 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2021601601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1010800830 + 1010800831.

It is an arithmetic number, because the mean of its divisors is an integer number (1010800831).

Almost surely, 2^2021601661 is an apocalyptic number.

It is an amenable number.

2021601661 is a deficient number, since it is larger than the sum of its proper divisors (1).

2021601661 is an equidigital number, since it uses as much as digits as its factorization.

2021601661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 864, while the sum is 25.

The square root of 2021601661 is about 44962.2248226219. The cubic root of 2021601661 is about 1264.4408806685.

Adding to 2021601661 its reverse (1661061202), we get a palindrome (3682662863).

The spelling of 2021601661 in words is "two billion, twenty-one million, six hundred one thousand, six hundred sixty-one".