1661500661 has 4 divisors (see below), whose sum is σ = 1759236012. Its totient is φ = 1563765312.

The previous prime is 1661500637. The next prime is 1661500663. The reversal of 1661500661 is 1660051661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1660051661 = 4751 ⋅349411.

It can be written as a sum of positive squares in 2 ways, for example, as 1369740100 + 291760561 = 37010^2 + 17081^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661500661 - 2¹⁸ = 1661238517 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 (1661500663) 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, 48867650 + ... + 48867683.

It is an arithmetic number, because the mean of its divisors is an integer number (439809003).

Almost surely, 2^1661500661 is an apocalyptic number.

It is an amenable number.

1661500661 is a deficient number, since it is larger than the sum of its proper divisors (97735351).

1661500661 is an equidigital number, since it uses as much as digits as its factorization.

1661500661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 97735350.

The product of its (nonzero) digits is 6480, while the sum is 32.

The square root of 1661500661 is about 40761.5095525178. The cubic root of 1661500661 is about 1184.4048382483.

The spelling of 1661500661 in words is "one billion, six hundred sixty-one million, five hundred thousand, six hundred sixty-one".