21006121 has 8 divisors (see below), whose sum is σ = 22318920. Its totient is φ = 19732608.

The previous prime is 21006119. The next prime is 21006137. The reversal of 21006121 is 12160012.

It can be written as a sum of positive squares in 4 ways, for example, as 13104400 + 7901721 = 3620^2 + 2811^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21006121 - 2¹ = 21006119 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21006151) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8716 + ... + 10861.

It is an arithmetic number, because the mean of its divisors is an integer number (2789865).

Almost surely, 2^21006121 is an apocalyptic number.

It is an amenable number.

21006121 is a deficient number, since it is larger than the sum of its proper divisors (1312799).

21006121 is a wasteful number, since it uses less digits than its factorization.

21006121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19643.

The product of its (nonzero) digits is 24, while the sum is 13.

The square root of 21006121 is about 4583.2435021500. The cubic root of 21006121 is about 275.9192203911.

Adding to 21006121 its reverse (12160012), we get a palindrome (33166133).

The spelling of 21006121 in words is "twenty-one million, six thousand, one hundred twenty-one".