1561440661 has 4 divisors (see below), whose sum is σ = 1703389824. Its totient is φ = 1419491500.

The previous prime is 1561440631. The next prime is 1561440677. The reversal of 1561440661 is 1660441651.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1561440661 - 2¹⁵ = 1561407893 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 (1561440631) 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, 70974565 + ... + 70974586.

It is an arithmetic number, because the mean of its divisors is an integer number (425847456).

Almost surely, 2^1561440661 is an apocalyptic number.

1561440661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1561440661 is a deficient number, since it is larger than the sum of its proper divisors (141949163).

1561440661 is a wasteful number, since it uses less digits than its factorization.

1561440661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 141949162.

The product of its (nonzero) digits is 17280, while the sum is 34.

The square root of 1561440661 is about 39515.0687839462. The cubic root of 1561440661 is about 1160.1349082592.

The spelling of 1561440661 in words is "one billion, five hundred sixty-one million, four hundred forty thousand, six hundred sixty-one".