1897991 has 2 divisors, whose sum is σ = 1897992. Its totient is φ = 1897990.

The previous prime is 1897979. The next prime is 1898009. The reversal of 1897991 is 1997981.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1897991 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1897691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 948995 + 948996.

It is an arithmetic number, because the mean of its divisors is an integer number (948996).

2^1897991 is an apocalyptic number.

1897991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1897991 is an equidigital number, since it uses as much as digits as its factorization.

1897991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 40824, while the sum is 44.

The square root of 1897991 is about 1377.6759415770. The cubic root of 1897991 is about 123.8125636781.

The spelling of 1897991 in words is "one million, eight hundred ninety-seven thousand, nine hundred ninety-one".