21312121 has 2 divisors, whose sum is σ = 21312122. Its totient is φ = 21312120.

The previous prime is 21312113. The next prime is 21312149. The reversal of 21312121 is 12121312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20430400 + 881721 = 4520^2 + 939^2 .

It is a cyclic number.

It is not a de Polignac number, because 21312121 - 2³ = 21312113 is a prime.

It is not a weakly prime, because it can be changed into another prime (21312721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10656060 + 10656061.

It is an arithmetic number, because the mean of its divisors is an integer number (10656061).

Almost surely, 2^21312121 is an apocalyptic number.

It is an amenable number.

21312121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21312121 is an equidigital number, since it uses as much as digits as its factorization.

21312121 is an evil number, because the sum of its binary digits is even.

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

The square root of 21312121 is about 4616.5052799710. The cubic root of 21312121 is about 277.2525554405.

Adding to 21312121 its reverse (12121312), we get a palindrome (33433433).

It can be divided in two parts, 21312 and 121, that multiplied together give a palindrome (2578752).

The spelling of 21312121 in words is "twenty-one million, three hundred twelve thousand, one hundred twenty-one".