991421831 has 4 divisors (see below), whose sum is σ = 1034527152. Its totient is φ = 948316512.

The previous prime is 991421813. The next prime is 991421839. The reversal of 991421831 is 138124199.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991421831 is a prime.

It is a super-2 number, since 2×991421831² = 1965834493966785122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991421839) 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, 21552626 + ... + 21552671.

It is an arithmetic number, because the mean of its divisors is an integer number (258631788).

Almost surely, 2^991421831 is an apocalyptic number.

991421831 is a deficient number, since it is larger than the sum of its proper divisors (43105321).

991421831 is a wasteful number, since it uses less digits than its factorization.

991421831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43105320.

The product of its digits is 15552, while the sum is 38.

The square root of 991421831 is about 31486.8517162323. The cubic root of 991421831 is about 997.1323950354.

The spelling of 991421831 in words is "nine hundred ninety-one million, four hundred twenty-one thousand, eight hundred thirty-one".