21217172 has 24 divisors (see below), whose sum is σ = 38769192. Its totient is φ = 10150400.

The previous prime is 21217159. The next prime is 21217187. The reversal of 21217172 is 27171212.

It can be written as a sum of positive squares in 4 ways, for example, as 1936 + 21215236 = 44^2 + 4606^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7472 + ... + 9912.

It is an arithmetic number, because the mean of its divisors is an integer number (1615383).

Almost surely, 2^21217172 is an apocalyptic number.

It is an amenable number.

21217172 is a deficient number, since it is larger than the sum of its proper divisors (17552020).

21217172 is a wasteful number, since it uses less digits than its factorization.

21217172 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2539 (or 2537 counting only the distinct ones).

The product of its digits is 392, while the sum is 23.

The square root of 21217172 is about 4606.2101558657. The cubic root of 21217172 is about 276.8402072470.

Adding to 21217172 its reverse (27171212), we get a palindrome (48388384).

It can be divided in two parts, 212 and 17172, that multiplied together give a square (3640464 = 1908²).

The spelling of 21217172 in words is "twenty-one million, two hundred seventeen thousand, one hundred seventy-two".