1851991 has 2 divisors, whose sum is σ = 1851992. Its totient is φ = 1851990.

The previous prime is 1851973. The next prime is 1852003. The reversal of 1851991 is 1991581.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1851991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1851901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 925995 + 925996.

It is an arithmetic number, because the mean of its divisors is an integer number (925996).

2^1851991 is an apocalyptic number.

1851991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1851991 is an equidigital number, since it uses as much as digits as its factorization.

1851991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 34.

The square root of 1851991 is about 1360.8787602134. The cubic root of 1851991 is about 122.8041256346.

The spelling of 1851991 in words is "one million, eight hundred fifty-one thousand, nine hundred ninety-one".