21787172 has 24 divisors (see below), whose sum is σ = 42938112. Its totient is φ = 9583200.

The previous prime is 21787169. The next prime is 21787177. The reversal of 21787172 is 27178712.

It is a Smith number, since the sum of its digits (35) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21787177) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6623 + ... + 9350.

It is an arithmetic number, because the mean of its divisors is an integer number (1789088).

Almost surely, 2^21787172 is an apocalyptic number.

21787172 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

21787172 is a deficient number, since it is larger than the sum of its proper divisors (21150940).

21787172 is a wasteful number, since it uses less digits than its factorization.

21787172 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16019 (or 16017 counting only the distinct ones).

The product of its digits is 10976, while the sum is 35.

The square root of 21787172 is about 4667.6730819542. The cubic root of 21787172 is about 279.2974393279.

The spelling of 21787172 in words is "twenty-one million, seven hundred eighty-seven thousand, one hundred seventy-two".