1991821553 has 2 divisors, whose sum is σ = 1991821554. Its totient is φ = 1991821552.

The previous prime is 1991821537. The next prime is 1991821561. The reversal of 1991821553 is 3551281991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1192459024 + 799362529 = 34532^2 + 28273^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991821553 - 2⁴ = 1991821537 is a prime.

It is not a weakly prime, because it can be changed into another prime (1991821523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995910776 + 995910777.

It is an arithmetic number, because the mean of its divisors is an integer number (995910777).

Almost surely, 2^1991821553 is an apocalyptic number.

It is an amenable number.

1991821553 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991821553 is an equidigital number, since it uses as much as digits as its factorization.

1991821553 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 97200, while the sum is 44.

The square root of 1991821553 is about 44629.8280637513. The cubic root of 1991821553 is about 1258.2013374090.

The spelling of 1991821553 in words is "one billion, nine hundred ninety-one million, eight hundred twenty-one thousand, five hundred fifty-three".