21721875 has 48 divisors (see below), whose sum is σ = 41497344. Its totient is φ = 9900000.

The previous prime is 21721873. The next prime is 21721879. The reversal of 21721875 is 57812712.

It is not a de Polignac number, because 21721875 - 2¹ = 21721873 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21721871) 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 47 ways as a sum of consecutive naturals, for example, 65460 + ... + 65790.

It is an arithmetic number, because the mean of its divisors is an integer number (864528).

Almost surely, 2^21721875 is an apocalyptic number.

21721875 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21721875 is a deficient number, since it is larger than the sum of its proper divisors (19775469).

21721875 is an frugal number, since it uses more digits than its factorization.

21721875 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 366 (or 346 counting only the distinct ones).

The product of its digits is 7840, while the sum is 33.

The square root of 21721875 is about 4660.6732346304. The cubic root of 21721875 is about 279.0181383616.

The spelling of 21721875 in words is "twenty-one million, seven hundred twenty-one thousand, eight hundred seventy-five".