1991372549 has 2 divisors, whose sum is σ = 1991372550. Its totient is φ = 1991372548.

The previous prime is 1991372533. The next prime is 1991372569. The reversal of 1991372549 is 9452731991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1396890625 + 594481924 = 37375^2 + 24382^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991372549 - 2⁴ = 1991372533 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 1991372497 and 1991372506.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991372569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995686274 + 995686275.

It is an arithmetic number, because the mean of its divisors is an integer number (995686275).

Almost surely, 2^1991372549 is an apocalyptic number.

It is an amenable number.

1991372549 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991372549 is an equidigital number, since it uses as much as digits as its factorization.

1991372549 is an evil number, because the sum of its binary digits is even.

The product of its digits is 612360, while the sum is 50.

The square root of 1991372549 is about 44624.7974673275. The cubic root of 1991372549 is about 1258.1067874584.

The spelling of 1991372549 in words is "one billion, nine hundred ninety-one million, three hundred seventy-two thousand, five hundred forty-nine".