1991707021 has 4 divisors (see below), whose sum is σ = 1991808000. Its totient is φ = 1991606044.

The previous prime is 1991707007. The next prime is 1991707027. The reversal of 1991707021 is 1207071991.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1207071991 = 349 ⋅3458659.

It is a cyclic number.

It is not a de Polignac number, because 1991707021 - 2¹¹ = 1991704973 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991707027) 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 in 3 ways as a sum of consecutive naturals, for example, 10171 + ... + 63928.

It is an arithmetic number, because the mean of its divisors is an integer number (497952000).

Almost surely, 2^1991707021 is an apocalyptic number.

It is an amenable number.

1991707021 is a deficient number, since it is larger than the sum of its proper divisors (100979).

1991707021 is an equidigital number, since it uses as much as digits as its factorization.

1991707021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 100978.

The product of its (nonzero) digits is 7938, while the sum is 37.

The square root of 1991707021 is about 44628.5449124212. The cubic root of 1991707021 is about 1258.1772209451.

The spelling of 1991707021 in words is "one billion, nine hundred ninety-one million, seven hundred seven thousand, twenty-one".