1561644901 has 4 divisors (see below), whose sum is σ = 1564905600. Its totient is φ = 1558384204.

The previous prime is 1561644883. The next prime is 1561644907. The reversal of 1561644901 is 1094461651.

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 1561644901 - 2⁹ = 1561644389 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 (1561644907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1629631 + ... + 1630588.

It is an arithmetic number, because the mean of its divisors is an integer number (391226400).

Almost surely, 2^1561644901 is an apocalyptic number.

It is an amenable number.

1561644901 is a deficient number, since it is larger than the sum of its proper divisors (3260699).

1561644901 is an equidigital number, since it uses as much as digits as its factorization.

1561644901 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3260698.

The product of its (nonzero) digits is 25920, while the sum is 37.

The square root of 1561644901 is about 39517.6530300067. The cubic root of 1561644901 is about 1160.1854888180.

The spelling of 1561644901 in words is "one billion, five hundred sixty-one million, six hundred forty-four thousand, nine hundred one".