1561665999 has 32 divisors (see below), whose sum is σ = 2145749760. Its totient is φ = 1010009088.

The previous prime is 1561665997. The next prime is 1561666003. The reversal of 1561665999 is 9995661651.

It is not a de Polignac number, because 1561665999 - 2¹ = 1561665997 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1561665991) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4423807 + ... + 4424159.

It is an arithmetic number, because the mean of its divisors is an integer number (67054680).

Almost surely, 2^1561665999 is an apocalyptic number.

1561665999 is a deficient number, since it is larger than the sum of its proper divisors (584083761).

1561665999 is a wasteful number, since it uses less digits than its factorization.

1561665999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 711.

The product of its digits is 3936600, while the sum is 57.

The square root of 1561665999 is about 39517.9199730957. The cubic root of 1561665999 is about 1160.1907135404.

It can be divided in two parts, 156166 and 5999, that added together give a triangular number (162165 = T₅₆₉).

The spelling of 1561665999 in words is "one billion, five hundred sixty-one million, six hundred sixty-five thousand, nine hundred ninety-nine".