20821640 has 32 divisors (see below), whose sum is σ = 53542080. Its totient is φ = 7138752.

The previous prime is 20821637. The next prime is 20821643. The reversal of 20821640 is 4612802.

It is an interprime number because it is at equal distance from previous prime (20821637) and next prime (20821643).

It is not an unprimeable number, because it can be changed into a prime (20821643) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 36902 + ... + 37461.

It is an arithmetic number, because the mean of its divisors is an integer number (1673190).

Almost surely, 2^20821640 is an apocalyptic number.

20821640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20821640 is an abundant number, since it is smaller than the sum of its proper divisors (32720440).

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

20821640 is a wasteful number, since it uses less digits than its factorization.

20821640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 74381 (or 74377 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 23.

The square root of 20821640 is about 4563.0735255965. The cubic root of 20821640 is about 275.1091137252.

The spelling of 20821640 in words is "twenty million, eight hundred twenty-one thousand, six hundred forty".