21721394 has 4 divisors (see below), whose sum is σ = 32582094. Its totient is φ = 10860696.

The previous prime is 21721387. The next prime is 21721397. The reversal of 21721394 is 49312712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 13965169 + 7756225 = 3737^2 + 2785^2 .

It is not an unprimeable number, because it can be changed into a prime (21721397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5430347 + ... + 5430350.

Almost surely, 2^21721394 is an apocalyptic number.

21721394 is a deficient number, since it is larger than the sum of its proper divisors (10860700).

21721394 is a wasteful number, since it uses less digits than its factorization.

21721394 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10860699.

The product of its digits is 3024, while the sum is 29.

The square root of 21721394 is about 4660.6216323576. The cubic root of 21721394 is about 279.0160788599.

The spelling of 21721394 in words is "twenty-one million, seven hundred twenty-one thousand, three hundred ninety-four".