21687172 has 24 divisors (see below), whose sum is σ = 43277976. Its totient is φ = 9420288.

The previous prime is 21687119. The next prime is 21687191. The reversal of 21687172 is 27178612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 8836 + 21678336 = 94^2 + 4656^2 .

It is a Harshad number since it is a multiple of its sum of digits (34).

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, 11383 + ... + 13150.

It is an arithmetic number, because the mean of its divisors is an integer number (1803249).

Almost surely, 2^21687172 is an apocalyptic number.

It is an amenable number.

21687172 is a deficient number, since it is larger than the sum of its proper divisors (21590804).

21687172 is a wasteful number, since it uses less digits than its factorization.

21687172 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24567 (or 24565 counting only the distinct ones).

The product of its digits is 9408, while the sum is 34.

The square root of 21687172 is about 4656.9487864910. The cubic root of 21687172 is about 278.8694721369.

The spelling of 21687172 in words is "twenty-one million, six hundred eighty-seven thousand, one hundred seventy-two".