21507172 has 6 divisors (see below), whose sum is σ = 37637558. Its totient is φ = 10753584.

The previous prime is 21507137. The next prime is 21507217. The reversal of 21507172 is 27170512.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 20124196 + 1382976 = 4486^2 + 1176^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2688393 + ... + 2688400.

Almost surely, 2^21507172 is an apocalyptic number.

It is an amenable number.

21507172 is a deficient number, since it is larger than the sum of its proper divisors (16130386).

21507172 is a wasteful number, since it uses less digits than its factorization.

21507172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5376797 (or 5376795 counting only the distinct ones).

The product of its (nonzero) digits is 980, while the sum is 25.

The square root of 21507172 is about 4637.5825599120. The cubic root of 21507172 is about 278.0958039798.

Adding to 21507172 its reverse (27170512), we get a palindrome (48677684).

The spelling of 21507172 in words is "twenty-one million, five hundred seven thousand, one hundred seventy-two".