21007121 has 6 divisors (see below), whose sum is σ = 22315830. Its totient is φ = 19771136.

The previous prime is 21007111. The next prime is 21007123. The reversal of 21007121 is 12170012.

It can be written as a sum of positive squares in 3 ways, for example, as 3900625 + 17106496 = 1975^2 + 4136^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21007121 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21007096 and 21007105.

It is not an unprimeable number, because it can be changed into a prime (21007123) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 36056 + ... + 36633.

It is an arithmetic number, because the mean of its divisors is an integer number (3719305).

Almost surely, 2^21007121 is an apocalyptic number.

It is an amenable number.

21007121 is a deficient number, since it is larger than the sum of its proper divisors (1308709).

21007121 is an equidigital number, since it uses as much as digits as its factorization.

21007121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72723 (or 72706 counting only the distinct ones).

The product of its (nonzero) digits is 28, while the sum is 14.

The square root of 21007121 is about 4583.3525938989. The cubic root of 21007121 is about 275.9235987156.

Adding to 21007121 its reverse (12170012), we get a palindrome (33177133).

The spelling of 21007121 in words is "twenty-one million, seven thousand, one hundred twenty-one".