991405 has 4 divisors (see below), whose sum is σ = 1189692. Its totient is φ = 793120.

The previous prime is 991387. The next prime is 991409. The reversal of 991405 is 504199.

991405 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 504199 = 37 ⋅13627.

It can be written as a sum of positive squares in 2 ways, for example, as 763876 + 227529 = 874^2 + 477^2 .

It is not a de Polignac number, because 991405 - 2⁹ = 990893 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 (991409) 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, 99136 + ... + 99145.

It is an arithmetic number, because the mean of its divisors is an integer number (297423).

2⁹⁹¹⁴⁰⁵ is an apocalyptic number.

It is an amenable number.

991405 is a deficient number, since it is larger than the sum of its proper divisors (198287).

991405 is a wasteful number, since it uses less digits than its factorization.

991405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 198286.

The product of its (nonzero) digits is 1620, while the sum is 28.

The square root of 991405 is about 995.6932258482. The cubic root of 991405 is about 99.7126752355.

The spelling of 991405 in words is "nine hundred ninety-one thousand, four hundred five".