991387 has 2 divisors, whose sum is σ = 991388. Its totient is φ = 991386.

The previous prime is 991381. The next prime is 991409. The reversal of 991387 is 783199.

991387 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991387 is a prime.

It is an Ulam number.

It is not a weakly prime, because it can be changed into another prime (991381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495693 + 495694.

It is an arithmetic number, because the mean of its divisors is an integer number (495694).

2⁹⁹¹³⁸⁷ is an apocalyptic number.

991387 is a deficient number, since it is larger than the sum of its proper divisors (1).

991387 is an equidigital number, since it uses as much as digits as its factorization.

991387 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13608, while the sum is 37.

The square root of 991387 is about 995.6841868786. The cubic root of 991387 is about 99.7120717690.

Subtracting from 991387 its product of digits (13608), we obtain a palindrome (977779).

It can be divided in two parts, 9913 and 87, that added together give a 4-th power (10000 = 10⁴).

The spelling of 991387 in words is "nine hundred ninety-one thousand, three hundred eighty-seven".