21720275 has 12 divisors (see below), whose sum is σ = 27862800. Its totient is φ = 16776480.

The previous prime is 21720247. The next prime is 21720277. The reversal of 21720275 is 57202712.

It is a de Polignac number, because none of the positive numbers 2^k-21720275 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21720277) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14255 + ... + 15704.

It is an arithmetic number, because the mean of its divisors is an integer number (2321900).

Almost surely, 2^21720275 is an apocalyptic number.

21720275 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21720275 is a deficient number, since it is larger than the sum of its proper divisors (6142525).

21720275 is a wasteful number, since it uses less digits than its factorization.

21720275 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29998 (or 29993 counting only the distinct ones).

The product of its (nonzero) digits is 1960, while the sum is 26.

The square root of 21720275 is about 4660.5015824480. The cubic root of 21720275 is about 279.0112875107.

Adding to 21720275 its reverse (57202712), we get a palindrome (78922987).

The spelling of 21720275 in words is "twenty-one million, seven hundred twenty thousand, two hundred seventy-five".