991721663 has 4 divisors (see below), whose sum is σ = 1043917560. Its totient is φ = 939525768.

The previous prime is 991721641. The next prime is 991721669. The reversal of 991721663 is 366127199.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 991721663 - 2¹² = 991717567 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 (991721669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26097920 + ... + 26097957.

It is an arithmetic number, because the mean of its divisors is an integer number (260979390).

Almost surely, 2^991721663 is an apocalyptic number.

991721663 is a deficient number, since it is larger than the sum of its proper divisors (52195897).

991721663 is a wasteful number, since it uses less digits than its factorization.

991721663 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52195896.

The product of its digits is 122472, while the sum is 44.

The square root of 991721663 is about 31491.6125817653. The cubic root of 991721663 is about 997.2329045786.

The spelling of 991721663 in words is "nine hundred ninety-one million, seven hundred twenty-one thousand, six hundred sixty-three".