1661261545 has 4 divisors (see below), whose sum is σ = 1993513860. Its totient is φ = 1329009232.

The previous prime is 1661261513. The next prime is 1661261587. The reversal of 1661261545 is 5451621661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5451621661 = 1499 ⋅3636839.

It can be written as a sum of positive squares in 2 ways, for example, as 945378009 + 715883536 = 30747^2 + 26756^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661261545 - 2⁵ = 1661261513 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 166126150 + ... + 166126159.

It is an arithmetic number, because the mean of its divisors is an integer number (498378465).

Almost surely, 2^1661261545 is an apocalyptic number.

It is an amenable number.

1661261545 is a deficient number, since it is larger than the sum of its proper divisors (332252315).

1661261545 is an equidigital number, since it uses as much as digits as its factorization.

1661261545 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 332252314.

The product of its digits is 43200, while the sum is 37.

The square root of 1661261545 is about 40758.5763367662. The cubic root of 1661261545 is about 1184.3480173792.

The spelling of 1661261545 in words is "one billion, six hundred sixty-one million, two hundred sixty-one thousand, five hundred forty-five".