2101656581 has 4 divisors (see below), whose sum is σ = 2122465164. Its totient is φ = 2080848000.

The previous prime is 2101656553. The next prime is 2101656617. The reversal of 2101656581 is 1856561012.

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 1658932900 + 442723681 = 40730^2 + 21041^2 .

It is a cyclic number.

It is not a de Polignac number, because 2101656581 - 2¹⁰ = 2101655557 is a prime.

It is a super-2 number, since 2×2101656581² = 8833920768921219122, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2101656511) 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, 10404140 + ... + 10404341.

It is an arithmetic number, because the mean of its divisors is an integer number (530616291).

Almost surely, 2^2101656581 is an apocalyptic number.

It is an amenable number.

2101656581 is a deficient number, since it is larger than the sum of its proper divisors (20808583).

2101656581 is a wasteful number, since it uses less digits than its factorization.

2101656581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20808582.

The product of its (nonzero) digits is 14400, while the sum is 35.

The square root of 2101656581 is about 45843.8281669409. The cubic root of 2101656581 is about 1280.9158039624.

The spelling of 2101656581 in words is "two billion, one hundred one million, six hundred fifty-six thousand, five hundred eighty-one".