491777821 has 4 divisors (see below), whose sum is σ = 503772444. Its totient is φ = 479783200.

The previous prime is 491777813. The next prime is 491777827. The reversal of 491777821 is 128777194.

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 167417721 + 324360100 = 12939^2 + 18010^2 .

It is a cyclic number.

It is not a de Polignac number, because 491777821 - 2³ = 491777813 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 (491777827) 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, 5997250 + ... + 5997331.

It is an arithmetic number, because the mean of its divisors is an integer number (125943111).

Almost surely, 2^491777821 is an apocalyptic number.

491777821 is a gapful number since it is divisible by the number (41) formed by its first and last digit.

It is an amenable number.

491777821 is a deficient number, since it is larger than the sum of its proper divisors (11994623).

491777821 is a wasteful number, since it uses less digits than its factorization.

491777821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11994622.

The product of its digits is 197568, while the sum is 46.

The square root of 491777821 is about 22176.0641458307. The cubic root of 491777821 is about 789.3258260516.

The spelling of 491777821 in words is "four hundred ninety-one million, seven hundred seventy-seven thousand, eight hundred twenty-one".