991381 has 2 divisors, whose sum is σ = 991382. Its totient is φ = 991380.

The previous prime is 991357. The next prime is 991387. The reversal of 991381 is 183199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 872356 + 119025 = 934^2 + 345^2 .

It is a cyclic number.

It is not a de Polignac number, because 991381 - 2¹³ = 983189 is a prime.

It is a super-2 number, since 2×991381² = 1965672574322, which contains 22 as substring.

991381 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991387) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495690 + 495691.

It is an arithmetic number, because the mean of its divisors is an integer number (495691).

2⁹⁹¹³⁸¹ is an apocalyptic number.

It is an amenable number.

991381 is a deficient number, since it is larger than the sum of its proper divisors (1).

991381 is an equidigital number, since it uses as much as digits as its factorization.

991381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1944, while the sum is 31.

The square root of 991381 is about 995.6811738704. The cubic root of 991381 is about 99.7118706119.

The spelling of 991381 in words is "nine hundred ninety-one thousand, three hundred eighty-one".