21721478 has 16 divisors (see below), whose sum is σ = 34627824. Its totient is φ = 10183680.

The previous prime is 21721477. The next prime is 21721489. The reversal of 21721478 is 87412712.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21721477) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9398 + ... + 11478.

It is an arithmetic number, because the mean of its divisors is an integer number (2164239).

Almost surely, 2^21721478 is an apocalyptic number.

21721478 is a deficient number, since it is larger than the sum of its proper divisors (12906346).

21721478 is a wasteful number, since it uses less digits than its factorization.

21721478 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2407.

The product of its digits is 6272, while the sum is 32.

The square root of 21721478 is about 4660.6306440223. The cubic root of 21721478 is about 279.0164385256.

The spelling of 21721478 in words is "twenty-one million, seven hundred twenty-one thousand, four hundred seventy-eight".