646776821 has 8 divisors (see below), whose sum is σ = 680421600. Its totient is φ = 613888240.

The previous prime is 646776817. The next prime is 646776833. The reversal of 646776821 is 128677646.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 646776821 - 2² = 646776817 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 (646776811) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 187295 + ... + 190716.

It is an arithmetic number, because the mean of its divisors is an integer number (85052700).

Almost surely, 2^646776821 is an apocalyptic number.

It is an amenable number.

646776821 is a deficient number, since it is larger than the sum of its proper divisors (33644779).

646776821 is a wasteful number, since it uses less digits than its factorization.

646776821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 378099.

The product of its digits is 677376, while the sum is 47.

The square root of 646776821 is about 25431.8072696378. The cubic root of 646776821 is about 864.8049148524.

The spelling of 646776821 in words is "six hundred forty-six million, seven hundred seventy-six thousand, eight hundred twenty-one".