1991947 has 2 divisors, whose sum is σ = 1991948. Its totient is φ = 1991946.

The previous prime is 1991933. The next prime is 1991959. The reversal of 1991947 is 7491991.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1991947 - 2⁷ = 1991819 is a prime.

It is a Chen prime.

It is an Ulam number.

1991947 is a lucky number.

It is a plaindrome in base 14.

It is not a weakly prime, because it can be changed into another prime (1991047) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995973 + 995974.

It is an arithmetic number, because the mean of its divisors is an integer number (995974).

2^1991947 is an apocalyptic number.

1991947 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991947 is an equidigital number, since it uses as much as digits as its factorization.

1991947 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20412, while the sum is 40.

The square root of 1991947 is about 1411.3635251061. The cubic root of 1991947 is about 125.8227751132.

The spelling of 1991947 in words is "one million, nine hundred ninety-one thousand, nine hundred forty-seven".