21172156 has 12 divisors (see below), whose sum is σ = 39001480. Its totient is φ = 10028880.

The previous prime is 21172153. The next prime is 21172187. The reversal of 21172156 is 65127112.

It is a self number, because there is not a number n which added to its sum of digits gives 21172156.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21172153) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 139215 + ... + 139366.

Almost surely, 2^21172156 is an apocalyptic number.

It is an amenable number.

21172156 is a deficient number, since it is larger than the sum of its proper divisors (17829324).

21172156 is a wasteful number, since it uses less digits than its factorization.

21172156 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 278604 (or 278602 counting only the distinct ones).

The product of its digits is 840, while the sum is 25.

The square root of 21172156 is about 4601.3211146365. The cubic root of 21172156 is about 276.6442800550.

Adding to 21172156 its reverse (65127112), we get a palindrome (86299268).

The spelling of 21172156 in words is "twenty-one million, one hundred seventy-two thousand, one hundred fifty-six".