820721808 has 180 divisors, whose sum is σ = 2476747728. Its totient is φ = 263088000.

The previous prime is 820721773. The next prime is 820721831. The reversal of 820721808 is 808127028.

It is a super-2 number, since 2×820721808² = 1347168572253577728, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 3269683 + ... + 3269933.

Almost surely, 2^820721808 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 820721808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1238373864).

820721808 is an abundant number, since it is smaller than the sum of its proper divisors (1656025920).

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

820721808 is a wasteful number, since it uses less digits than its factorization.

820721808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 332 (or 285 counting only the distinct ones).

The product of its (nonzero) digits is 14336, while the sum is 36.

The square root of 820721808 is about 28648.2426686176. The cubic root of 820721808 is about 936.2647180252.

The spelling of 820721808 in words is "eight hundred twenty million, seven hundred twenty-one thousand, eight hundred eight".