21172738 has 4 divisors (see below), whose sum is σ = 31759110. Its totient is φ = 10586368.

The previous prime is 21172733. The next prime is 21172757. The reversal of 21172738 is 83727112.

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., 16916769 + 4255969 = 4113^2 + 2063^2 .

It is not an unprimeable number, because it can be changed into a prime (21172733) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5293183 + ... + 5293186.

Almost surely, 2^21172738 is an apocalyptic number.

21172738 is a deficient number, since it is larger than the sum of its proper divisors (10586372).

21172738 is a wasteful number, since it uses less digits than its factorization.

21172738 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10586371.

The product of its digits is 4704, while the sum is 31.

The square root of 21172738 is about 4601.3843569083. The cubic root of 21172738 is about 276.6468149173.

The spelling of 21172738 in words is "twenty-one million, one hundred seventy-two thousand, seven hundred thirty-eight".