21730121 has 12 divisors (see below), whose sum is σ = 25461888. Its totient is φ = 18158592.

The previous prime is 21730109. The next prime is 21730133. The reversal of 21730121 is 12103712.

It is an interprime number because it is at equal distance from previous prime (21730109) and next prime (21730133).

It is not a de Polignac number, because 21730121 - 2⁶ = 21730057 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21730121.

It is not an unprimeable number, because it can be changed into a prime (21730021) 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, 84425 + ... + 84681.

It is an arithmetic number, because the mean of its divisors is an integer number (2121824).

Almost surely, 2^21730121 is an apocalyptic number.

It is an amenable number.

21730121 is a deficient number, since it is larger than the sum of its proper divisors (3731767).

21730121 is an frugal number, since it uses more digits than its factorization.

21730121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 568 (or 311 counting only the distinct ones).

The product of its (nonzero) digits is 84, while the sum is 17.

The square root of 21730121 is about 4661.5577868348. The cubic root of 21730121 is about 279.0534406010.

Adding to 21730121 its reverse (12103712), we get a palindrome (33833833).

The spelling of 21730121 in words is "twenty-one million, seven hundred thirty thousand, one hundred twenty-one".