21217121 has 2 divisors, whose sum is σ = 21217122. Its totient is φ = 21217120.

The previous prime is 21217117. The next prime is 21217151. The reversal of 21217121 is 12171212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21160000 + 57121 = 4600^2 + 239^2 .

It is a cyclic number.

It is not a de Polignac number, because 21217121 - 2² = 21217117 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21217121.

It is not a weakly prime, because it can be changed into another prime (21217111) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10608560 + 10608561.

It is an arithmetic number, because the mean of its divisors is an integer number (10608561).

Almost surely, 2^21217121 is an apocalyptic number.

It is an amenable number.

21217121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21217121 is an equidigital number, since it uses as much as digits as its factorization.

21217121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 56, while the sum is 17.

The square root of 21217121 is about 4606.2046198579. The cubic root of 21217121 is about 276.8399854319.

Adding to 21217121 its reverse (12171212), we get a palindrome (33388333).

The spelling of 21217121 in words is "twenty-one million, two hundred seventeen thousand, one hundred twenty-one".