1991964521 has 4 divisors (see below), whose sum is σ = 2011687044. Its totient is φ = 1972242000.

The previous prime is 1991964517. The next prime is 1991964529. The reversal of 1991964521 is 1254691991.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1629252496 + 362712025 = 40364^2 + 19045^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991964521 - 2² = 1991964517 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1991964529) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9861110 + ... + 9861311.

It is an arithmetic number, because the mean of its divisors is an integer number (502921761).

Almost surely, 2^1991964521 is an apocalyptic number.

It is an amenable number.

1991964521 is a deficient number, since it is larger than the sum of its proper divisors (19722523).

1991964521 is a wasteful number, since it uses less digits than its factorization.

1991964521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19722522.

The product of its digits is 174960, while the sum is 47.

The square root of 1991964521 is about 44631.4297440716. The cubic root of 1991964521 is about 1258.2314402103.

The spelling of 1991964521 in words is "one billion, nine hundred ninety-one million, nine hundred sixty-four thousand, five hundred twenty-one".