668921820 has 48 divisors (see below), whose sum is σ = 2140551168. Its totient is φ = 152896320.

The previous prime is 668921783. The next prime is 668921821. The reversal of 668921820 is 28129866.

It is a super-2 number, since 2×668921820² = 894912802544224800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668921821) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 795916 + ... + 796755.

It is an arithmetic number, because the mean of its divisors is an integer number (44594816).

Almost surely, 2^668921820 is an apocalyptic number.

668921820 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

668921820 is an abundant number, since it is smaller than the sum of its proper divisors (1471629348).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

668921820 is a wasteful number, since it uses less digits than its factorization.

668921820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1592690 (or 1592688 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 42.

The square root of 668921820 is about 25863.5229618859. The cubic root of 668921820 is about 874.5643850718.

The spelling of 668921820 in words is "six hundred sixty-eight million, nine hundred twenty-one thousand, eight hundred twenty".