1661522581 has 4 divisors (see below), whose sum is σ = 1702047564. Its totient is φ = 1620997600.

The previous prime is 1661522573. The next prime is 1661522633. The reversal of 1661522581 is 1852251661.

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 145588356 + 1515934225 = 12066^2 + 38935^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661522581 - 2³ = 1661522573 is a prime.

It is a super-2 number, since 2×1661522581² = 5521314574345803122, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1661522581.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661522381) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 20262430 + ... + 20262511.

It is an arithmetic number, because the mean of its divisors is an integer number (425511891).

Almost surely, 2^1661522581 is an apocalyptic number.

It is an amenable number.

1661522581 is a deficient number, since it is larger than the sum of its proper divisors (40524983).

1661522581 is an equidigital number, since it uses as much as digits as its factorization.

1661522581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40524982.

The product of its digits is 28800, while the sum is 37.

The square root of 1661522581 is about 40761.7784327426. The cubic root of 1661522581 is about 1184.4100468007.

The spelling of 1661522581 in words is "one billion, six hundred sixty-one million, five hundred twenty-two thousand, five hundred eighty-one".