991641551 has 4 divisors (see below), whose sum is σ = 1018442712. Its totient is φ = 964840392.

The previous prime is 991641517. The next prime is 991641577. The reversal of 991641551 is 155146199.

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 991641551 - 2¹⁸ = 991379407 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 991641499 and 991641508.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991649551) 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, 13400525 + ... + 13400598.

It is an arithmetic number, because the mean of its divisors is an integer number (254610678).

Almost surely, 2^991641551 is an apocalyptic number.

991641551 is a deficient number, since it is larger than the sum of its proper divisors (26801161).

991641551 is a wasteful number, since it uses less digits than its factorization.

991641551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26801160.

The product of its digits is 48600, while the sum is 41.

The square root of 991641551 is about 31490.3405983486. The cubic root of 991641551 is about 997.2060514549.

The spelling of 991641551 in words is "nine hundred ninety-one million, six hundred forty-one thousand, five hundred fifty-one".