961644721 has 4 divisors (see below), whose sum is σ = 964400500. Its totient is φ = 958888944.

The previous prime is 961644713. The next prime is 961644731. The reversal of 961644721 is 127446169.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127446169 = 1097 ⋅116177.

It can be written as a sum of positive squares in 2 ways, for example, as 428034721 + 533610000 = 20689^2 + 23100^2 .

It is a cyclic number.

It is not a de Polignac number, because 961644721 - 2³ = 961644713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (961644731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1377366 + ... + 1378063.

It is an arithmetic number, because the mean of its divisors is an integer number (241100125).

Almost surely, 2^961644721 is an apocalyptic number.

It is an amenable number.

961644721 is a deficient number, since it is larger than the sum of its proper divisors (2755779).

961644721 is a wasteful number, since it uses less digits than its factorization.

961644721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2755778.

The product of its digits is 72576, while the sum is 40.

The square root of 961644721 is about 31010.3969823026. The cubic root of 961644721 is about 987.0478736967.

The spelling of 961644721 in words is "nine hundred sixty-one million, six hundred forty-four thousand, seven hundred twenty-one".