21721754 has 16 divisors (see below), whose sum is σ = 33868800. Its totient is φ = 10435824.

The previous prime is 21721747. The next prime is 21721781. The reversal of 21721754 is 45712712.

It is a Harshad number since it is a multiple of its sum of digits (29).

It is a Curzon number.

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 7 ways as a sum of consecutive naturals, for example, 13079 + ... + 14645.

It is an arithmetic number, because the mean of its divisors is an integer number (2116800).

Almost surely, 2^21721754 is an apocalyptic number.

21721754 is a deficient number, since it is larger than the sum of its proper divisors (12147046).

21721754 is a wasteful number, since it uses less digits than its factorization.

21721754 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1837.

The product of its digits is 3920, while the sum is 29.

The square root of 21721754 is about 4660.6602536551. The cubic root of 21721754 is about 279.0176202778.

The spelling of 21721754 in words is "twenty-one million, seven hundred twenty-one thousand, seven hundred fifty-four".