21172056 has 16 divisors (see below), whose sum is σ = 52930200. Its totient is φ = 7057344.

The previous prime is 21172037. The next prime is 21172057. The reversal of 21172056 is 65027112.

It is a Harshad number since it is a multiple of its sum of digits (24), and also a Moran number because the ratio is a prime number: 882169 = 21172056 / (2 + 1 + 1 + 7 + 2 + 0 + 5 + 6).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21172057) 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 3 ways as a sum of consecutive naturals, for example, 441061 + ... + 441108.

Almost surely, 2^21172056 is an apocalyptic number.

It is an amenable number.

21172056 is an abundant number, since it is smaller than the sum of its proper divisors (31758144).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21172056 is a wasteful number, since it uses less digits than its factorization.

21172056 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 882178 (or 882174 counting only the distinct ones).

The product of its (nonzero) digits is 840, while the sum is 24.

The square root of 21172056 is about 4601.3102481793. The cubic root of 21172056 is about 276.6438445070.

Adding to 21172056 its reverse (65027112), we get a palindrome (86199168).

The spelling of 21172056 in words is "twenty-one million, one hundred seventy-two thousand, fifty-six".