21171728 has 10 divisors (see below), whose sum is σ = 41020254. Its totient is φ = 10585856.

The previous prime is 21171727. The next prime is 21171739. The reversal of 21171728 is 82717112.

It can be written as a sum of positive squares in only one way, i.e., 21086464 + 85264 = 4592^2 + 292^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21171728.

It is not an unprimeable number, because it can be changed into a prime (21171727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 661601 + ... + 661632.

Almost surely, 2^21171728 is an apocalyptic number.

It is an amenable number.

21171728 is a deficient number, since it is larger than the sum of its proper divisors (19848526).

21171728 is a wasteful number, since it uses less digits than its factorization.

21171728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1323241 (or 1323235 counting only the distinct ones).

The product of its digits is 1568, while the sum is 29.

The square root of 21171728 is about 4601.2746060195. The cubic root of 21171728 is about 276.6424158999.

The spelling of 21171728 in words is "twenty-one million, one hundred seventy-one thousand, seven hundred twenty-eight".