1991943901 has 2 divisors, whose sum is σ = 1991943902. Its totient is φ = 1991943900.

The previous prime is 1991943887. The next prime is 1991943923. The reversal of 1991943901 is 1093491991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1913975001 + 77968900 = 43749^2 + 8830^2 .

It is an emirp because it is prime and its reverse (1093491991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1991943901 - 2¹³ = 1991935709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991949901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995971950 + 995971951.

It is an arithmetic number, because the mean of its divisors is an integer number (995971951).

Almost surely, 2^1991943901 is an apocalyptic number.

It is an amenable number.

1991943901 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991943901 is an equidigital number, since it uses as much as digits as its factorization.

1991943901 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 78732, while the sum is 46.

The square root of 1991943901 is about 44631.1987403431. The cubic root of 1991943901 is about 1258.2270986300.

The spelling of 1991943901 in words is "one billion, nine hundred ninety-one million, nine hundred forty-three thousand, nine hundred one".