21721275 has 36 divisors (see below), whose sum is σ = 40960920. Its totient is φ = 10972800.

The previous prime is 21721253. The next prime is 21721277. The reversal of 21721275 is 57212712.

It is not a de Polignac number, because 21721275 - 2⁶ = 21721211 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21721277) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 1735 + ... + 6815.

Almost surely, 2^21721275 is an apocalyptic number.

21721275 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21721275 is a deficient number, since it is larger than the sum of its proper divisors (19239645).

21721275 is a wasteful number, since it uses less digits than its factorization.

21721275 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5116 (or 5108 counting only the distinct ones).

The product of its digits is 1960, while the sum is 27.

The square root of 21721275 is about 4660.6088658028. The cubic root of 21721275 is about 279.0155693319.

Adding to 21721275 its reverse (57212712), we get a palindrome (78933987).

The spelling of 21721275 in words is "twenty-one million, seven hundred twenty-one thousand, two hundred seventy-five".