999961561 has 4 divisors (see below), whose sum is σ = 1000930612. Its totient is φ = 998992512.

The previous prime is 999961541. The next prime is 999961577. The reversal of 999961561 is 165169999.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165169999 = 997 ⋅165667.

It can be written as a sum of positive squares in 2 ways, for example, as 826907536 + 173054025 = 28756^2 + 13155^2 .

It is a cyclic number.

It is not a de Polignac number, because 999961561 - 2⁷ = 999961433 is a prime.

It is a pancake number, because a pancake can be divided into 999961561 parts by 44720 straight cuts.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (999961511) 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, 482976 + ... + 485041.

It is an arithmetic number, because the mean of its divisors is an integer number (250232653).

Almost surely, 2^999961561 is an apocalyptic number.

It is an amenable number.

999961561 is a deficient number, since it is larger than the sum of its proper divisors (969051).

999961561 is a wasteful number, since it uses less digits than its factorization.

999961561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 969050.

The product of its digits is 1180980, while the sum is 55.

The square root of 999961561 is about 31622.1688218882. The cubic root of 999961561 is about 999.9871868358.

The spelling of 999961561 in words is "nine hundred ninety-nine million, nine hundred sixty-one thousand, five hundred sixty-one".