19856891 has 2 divisors, whose sum is σ = 19856892. Its totient is φ = 19856890.

The previous prime is 19856869. The next prime is 19856897. The reversal of 19856891 is 19865891.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19856891 is a prime.

It is a super-2 number, since 2×19856891² = 788592240371762, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (19856897) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9928445 + 9928446.

It is an arithmetic number, because the mean of its divisors is an integer number (9928446).

Almost surely, 2^19856891 is an apocalyptic number.

19856891 is a deficient number, since it is larger than the sum of its proper divisors (1).

19856891 is an equidigital number, since it uses as much as digits as its factorization.

19856891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 155520, while the sum is 47.

The square root of 19856891 is about 4456.1071575984. The cubic root of 19856891 is about 270.7927819575.

The spelling of 19856891 in words is "nineteen million, eight hundred fifty-six thousand, eight hundred ninety-one".