21721270 has 16 divisors (see below), whose sum is σ = 39156048. Its totient is φ = 8675680.

The previous prime is 21721253. The next prime is 21721277. The reversal of 21721270 is 7212712.

It is a congruent number.

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

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8592 + ... + 10828.

It is an arithmetic number, because the mean of its divisors is an integer number (2447253).

Almost surely, 2^21721270 is an apocalyptic number.

21721270 is a deficient number, since it is larger than the sum of its proper divisors (17434778).

21721270 is a wasteful number, since it uses less digits than its factorization.

21721270 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3215.

The product of its (nonzero) digits is 392, while the sum is 22.

The square root of 21721270 is about 4660.6083293922. The cubic root of 21721270 is about 279.0155479232.

Adding to 21721270 its reverse (7212712), we get a palindrome (28933982).

The spelling of 21721270 in words is "twenty-one million, seven hundred twenty-one thousand, two hundred seventy".