19851991 has 2 divisors, whose sum is σ = 19851992. Its totient is φ = 19851990.

The previous prime is 19851983. The next prime is 19852003. The reversal of 19851991 is 19915891.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 19851991 - 2³ = 19851983 is a prime.

It is a congruent number.

It is a weakly prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9925995 + 9925996.

It is an arithmetic number, because the mean of its divisors is an integer number (9925996).

Almost surely, 2^19851991 is an apocalyptic number.

19851991 is a deficient number, since it is larger than the sum of its proper divisors (1).

19851991 is an equidigital number, since it uses as much as digits as its factorization.

19851991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 29160, while the sum is 43.

The square root of 19851991 is about 4455.5573164308. The cubic root of 19851991 is about 270.7705059999.

The spelling of 19851991 in words is "nineteen million, eight hundred fifty-one thousand, nine hundred ninety-one".