21875721 has 8 divisors (see below), whose sum is σ = 33334464. Its totient is φ = 12500400.

The previous prime is 21875713. The next prime is 21875747. The reversal of 21875721 is 12757812.

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

It is not a de Polignac number, because 21875721 - 2³ = 21875713 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21871721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 520830 + ... + 520871.

It is an arithmetic number, because the mean of its divisors is an integer number (4166808).

Almost surely, 2^21875721 is an apocalyptic number.

21875721 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21875721 is a deficient number, since it is larger than the sum of its proper divisors (11458743).

21875721 is a wasteful number, since it uses less digits than its factorization.

21875721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1041711.

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

The square root of 21875721 is about 4677.1488109745. The cubic root of 21875721 is about 279.6753081522.

The spelling of 21875721 in words is "twenty-one million, eight hundred seventy-five thousand, seven hundred twenty-one".