991564761 has 16 divisors (see below), whose sum is σ = 1518186240. Its totient is φ = 569319120.

The previous prime is 991564759. The next prime is 991564789. The reversal of 991564761 is 167465199.

It is a happy number.

It is not a de Polignac number, because 991564761 - 2¹ = 991564759 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 991564761.

It is not an unprimeable number, because it can be changed into a prime (991564741) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 790095 + ... + 791348.

It is an arithmetic number, because the mean of its divisors is an integer number (94886640).

Almost surely, 2^991564761 is an apocalyptic number.

It is an amenable number.

991564761 is a deficient number, since it is larger than the sum of its proper divisors (526621479).

991564761 is a wasteful number, since it uses less digits than its factorization.

991564761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1581476.

The product of its digits is 408240, while the sum is 48.

The square root of 991564761 is about 31489.1213119706. The cubic root of 991564761 is about 997.1803104905.

The spelling of 991564761 in words is "nine hundred ninety-one million, five hundred sixty-four thousand, seven hundred sixty-one".